High temperature thin film property measurement system and method

ABSTRACT

A system and method for measuring lubricant thickness and degradation, carbon wear and carbon thickness, and surface roughness and debris on thin film magnetic disks at angles that are not substantially Brewster&#39;s angle of the thin film (carbon) protective overcoat in a high temperature environment. A focused optical light whose polarization can be switched between P or S polarization is incident at an angle to the surface of the thin film magnetic disk. The polarization switch can be accomplished using a temperature compensated quartz half plate. The range of angles can be from zero degrees from normal to near Brewster&#39;s angle and from an angle greater than Brewster&#39;s angle to 90 degrees. This range of angles allows the easy measurement of the change in lubricant thickness due to the interaction of the thin film head, the absolute lubricant thickness and degradation of the lubricant. It also allows the measurement of changes in carbon thickness and the absolute carbon thickness. The surface roughness can also be measured at any of the angles specified above.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 09/136,897 filed Aug. 19, 1998, which claims priority from U.S.provisional application No. 60/059,740 filed Sep. 22, 1997 which areboth incorporated by reference herein in their entirety. Thisapplication is also related to U.S. patent application Ser. No.09/376,152, titled “System and Method for Measuring Thin Film Propertiesand Analyzing Two-Dimensional Histograms Using a Symmetry Operation”filed on Aug. 17, 1999, and to U.S. patent application Ser. No.09/376,705, titled “System and Method for Measuring Thin Film Propertiesand Analyzing Two-Dimensional Histograms Using a Subtraction Operation”,filed on Aug. 17, 1999, and to U.S. patent application Ser. No.09.376,151, titled “System and Method for Measuring Thin Film Propertiesand Analyzing Two-Dimensional Histograms Using AND/NOT Operations”,filed on Aug. 17, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed toward measuring thin films and moreparticularly toward measuring lubricant thickness, lubricantdegradation, thin film thickness and wear, and surface roughness using alaser directed toward a thin film disk at many angles includingnon-Brewster's angles of an absorbing layer of the thin film.

2. Description of Background Art

Coated thin film disks are used in a variety of industries. One exampleis the computer hard disk industry. A computer hard disk (magneticstorage device) is a non-volatile memory device that can store largeamounts of data. One problem that the manufacturers of hard disksexperience is how to maximize the operating life of a hard disk. When ahard disk fails the data stored therein may be difficult, expensive, orimpossible to retrieve.

A schematic of a thin film disk used in magnetic storage devices isshown in FIG. 1. It includes a magnetic thin film (layer) 106 which isdeposited upon a substrate 108 (typically a NiP plated Al—Mg alloy orglass). The magnetic thin film 106 can be protected by a thin film ofcarbon 104 (carbon layer), for example, whose thickness is typically 50to 200 Angstroms (Å). The carbon layer 104 is typically coated with athin layer (10 to 30 Angstroms) of a fluorocarbon lubricant 102(lubricant layer). The lubricant layer 102 serves to increase thedurability of the underlying carbon layer 104 particularly when themagnetic read/write head contacts the disk, for example when the diskdrive is turned off, as described below. During the development andtesting of thin film disks it is necessary to subject thin film magneticdisks to numerous starts and stops of the read/write head. Thestart/stops cause the read/write head to contact the thin film disk 100in a dedicated region of the thin film disk 100 known as the start/stopzone. The action of stopping and starting the thin film head on thestart/stop zone can cause depletion and/or degradation of thefluorocarbon lubricant layer 102, wear of the carbon layer 104 andchanges in the surface roughness. A conventional technique for measuringthin film characteristics are discussed in U.S. Pat. No. 4,873,430 whichis incorporated by reference herein in its entirety. This patentdescribes a technique that uses a P polarized collimated (unfocussed)laser propagating at the Brewster's angle of the film to measure filmthickness and surface roughness.

U.S. Pat. No. 5,726,455 describes an optical system for measuring onlythe specular component of light reflected from a thin film magneticdisk. The patent purports that the system is able to measure lubricantcoating thickness and coating wear. This system uses a temperaturestabilized (Peltier effect cooled) light source and an integratingsphere detector which is remotely located from the disk. The angle ofincidence is between the Brewster's angle of the lubricant and that ofthe adjacent layer. This invention makes no provision for themeasurement of the scattered light nor does it measure surfaceroughness.

Other techniques for measuring surface roughness are discussed in U.S.Pat. Nos. 5,608,527, 5,196,906, 5,313,542, 4,668,860, 5,406,082 and inthe book “Optical Scattering-Measurement and Analysis” second edition byJohn C. Stover, SPIE Press, Bellingham, Wash., 1995 on page 169 through170, which are all incorporated by reference herein in their entirety.These references relate to obtaining the surface roughness and do notaddress identifying lubricant thickness and degradation or thin filmthickness or wear.

Specifically, U.S. Pat. No. 5,608,527 describes a technique formeasuring the specular and scattered light in one scattering plane byusing a multi-segmented array. The specular and scattered lights areused to obtain the surface roughness. U.S. Pat. No. 5,196,906 describesa modular scatterometer for determining surface roughness from an arrayof detectors positioned along a hemisphere. U.S. Pat. No. 5,313,542describes a scatterometer which uses depolarized light from a laserdiode and fiber optic bundles to collect partial or full hemisphericallyscattered light. U.S. Pat. No. 4,668,860 describes a scatterometer forevaluating the surface quality of an optical element which has both bulkand surface scatter. This patent describes a technique that purports toseparate surface and bulk scatter by using the polarizationcharacteristics of the light. U.S. Pat. No. 5,406,082 describes asurface inspection and characterization system that uses a broadbandinfrared light source which is directed onto the surface to beinspected. The reflected light is separated into several wavelengths andthese signals are used to characterize the surface by such properties asabsorbency.

A technique for combining the measurement of thin film thickness andsurface roughness is described in a brochure by AHEAD Optoelectronics,Inc., Taipei, Taiwan, R.O.C, which is incorporated by reference hereinin its entirety. This describes an instrument called an IntegratingSphere Ellipsometry Analyzer. This instrument is a combined ellipsometerand integrating sphere analyzer. This brochure teaches a measurementtechnique that uses an ellipsometric technique for the ex situmeasurement of absolute film thickness and indices of refraction. Thistechnique also uses an integrating sphere to measure surfacemicroroughness at a variable angle. The system as described is designedfor ex situ measurement of film thickness and surface microroughness, itis not capable of measuring in situ wear, lubricant and surfaceroughness.

A technique for measuring thin film properties at Brewster's angle isdescribed in S. Meeks et. al., Optical Surface Analysis of theHead-Disk-Interface of Thin Film Disks, ASME Transactions on Tribology,Vol. 117, pp. 112-118, (Janurary 1995), which is incorporated byreference herein in its entirety.

None of these references teach a single system and method for performingall of these measurements in situ. In addition, references Meeks et al.and Juliana et al. teach that the measurement should occur atsubstantially Brewster's angle of the carbon 104. U.S. Pat. No.5,726,455 teaches that the measurement should occur between Brewster'sangle of the lubricant and that of the adjacent layer. A stated benefitof using this angle is that the light signal will not reflect off of thecarbon 104 and instead will pass directly through the carbon 104 andreflect off of the magnetic layer 106.

What is needed is a system and method for examining thin film disksthat: (1) measures the amount of lubricant thickness and thicknesschange; (2) measures the extent of lubricant degradation; (3) measuresthe wear and thickness of the carbon layer; (4) measures the absolutesurface roughness and changes in the surface roughness; and (5) enablesthese measurements to be (a) performed simultaneously, (b) performed atan angle of incidence that is substantially different from Brewster'sangle, and (c) performed in situ or ex situ.

SUMMARY OF THE INVENTION

The invention is a system and method for measuring thin film diskproperties using an optical system that transmits electromagneticradiation toward the thin film disk at an angle of incidence that neednot be substantially Brewster's angle. The present invention measureslubricant thickness and degradation, carbon wear and thickness, andsurface roughness of thin film magnetic disks at angles that are notsubstantially Brewster's angle of the thin film protective overcoat(carbon). A focused optical light whose polarization can be switchedbetween P or S polarization is incident at an angle to the surface ofthe thin film magnetic disk. This allows the easy measurement of thechange in lubricant thickness due to the interaction of the thin filmhead, the absolute lubricant thickness and degradation of the lubricant.It also allows the measurement of changes in carbon thickness and theabsolute carbon thickness. The surface roughness can also be measured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a thin film that can be measured using thepreferred embodiment of the present invention.

FIG. 2 is an illustration of an apparatus for measuring properties ofthe thin film according to the preferred embodiment of the presentinvention.

FIG. 3 is a more detailed illustration of a liquid crystal variableretarder (LCVR) driver according to the preferred embodiment of thepresent invention.

FIG. 4 is an illustration of the feedback amplification system of thepreferred embodiment of the present invention.

FIGS. 5(a)-(c) are illustrations of the reflective and scatteringproperties of P and S polarized radiation according to the preferredembodiment of the present invention.

FIG. 6 is a more detailed illustration of photodiode electronicsaccording to the preferred embodiment of the present invention.

FIG. 7 is a flow chart illustrating a method for measuring in situ thinfilm properties according to the preferred embodiment of the presentinvention.

FIG. 8 is a graph illustrating the reflectance of P and S polarizedradiation versus angle of incidence off a thin film having no lubricantand having ten nanometers of lubricant according to the preferredembodiment of the present invention.

FIG. 9 is a graph illustrating the reflectance of P and S polarizedradiation versus angle of incidence off a thin film having twentynanometers of carbon and having fifteen nanometers of carbon accordingto the preferred embodiment of the present invention.

FIG. 10 is a two dimensional concentration histogram illustrating therelationship between changes in S polarized radiation and P polarizedradiation with respect to thin film measurements when an angle ofincidence of the radiation source is between 53 degrees and 71 degreesaccording to one embodiment of the present invention.

FIG. 11 is a two dimensional concentration histogram illustrating therelationship between changes in S polarized radiation and P polarizedradiation with respect to thin film measurements when an angle ofincidence of the radiation source is approximately 53 degrees accordingto one embodiment of the present invention.

FIG. 12 is a two dimensional concentration histogram illustrating therelationship between changes in S polarized radiation and P polarizedradiation with respect to thin film measurements when an angle ofincidence of the radiation source is less than 53 degrees according toone embodiment of the present invention.

FIG. 13 is a two dimensional concentration histogram illustrating therelationship between changes in S polarized radiation and P polarizedradiation with respect to thin film measurements when an angle ofincidence of the radiation source is between 71 degrees and 90 degreesaccording to one embodiment of the present invention.

FIG. 14 is a theoretical graph illustrating the change in P specularreflectivity verses the thickness of a carbon layer in nanometers (nm).

FIG. 15 is a graph illustrating the sensitivity of P polarized lightreflectivity to carbon wear verses the k of carbon for a light signalhaving a wavelength of 650 nm and having an angle of incidence of 58degrees.

FIG. 16 is an illustration of a two dimensional fast Fourier transformof a S specular image as measured by the preferred embodiment of thepresent invention.

FIG. 17 is an illustration of a cut through the fast Fourier transformshowing the texture angles, width and texture amplitude distribution ofa disk texture line pattern.

FIG. 18 is a flow chart illustrating a method for measuring carbon wearfor an in situ process according to an embodiment of the presentinvention.

FIG. 19 is a flow chart illustrating a method for measuring carbon wearfor an ex situ process according to an embodiment of the presentinvention.

FIG. 20 is an illustration of a high temperature thin film measurementsystem 2000 according to one embodiment of the present invention.

FIG. 21 is an illustration of a computer system according to anembodiment of the present invention.

FIG. 22 is a flowchart illustrating the operation of the symmetry unit2112 according to one embodiment of the present invention.

FIG. 23 is a flow chart illustrating the operation of the histogramsubtraction unit 2114 according to one embodiment of the presentinvention.

FIG. 24 is a flow chart illustrating the operation of the AND/NOT unit2116 according to one embodiment of the present invention.

FIG. 25 is an example of a simplified two-dimensional (2D) histogramimage according to an embodiment of the present invention.

FIG. 26 is a chart illustrating an analysis technique according to oneembodiment of the present invention.

FIG. 27 illustrates one example of histogram analysis according to theAND/NOT unit of the present invention.

FIG. 28 illustrates one example of histogram analysis using P specularor S specular versus P scattered or S scattered variable according tothe AND/NOT unit of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention is now described withreference to the figures where like reference numbers indicate identicalor functionally similar elements. Also in the figures, the left mostdigit(s) of each reference number correspond(s) to the figure in whichthe reference number is first used.

FIG. 2 is an illustration of an apparatus for measuring properties ofthe thin film according to the preferred embodiment of the presentinvention. The apparatus uses a focused laser light signal whose angleof propagation can be between zero degrees from normal and ninetydegrees from normal.

One embodiment of the apparatus 200 includes a conventional laser diode202, e.g., SLD 104AU available from Sony, Tokyo, Japan, which has beencollimated by Hoetron Corp., Sunnyvale, Calif., e.g., a conventionallinear polarizer 204, e.g., made of Polarcor that is commerciallyavailable from Newport Corp., Irvine, Calif., a conventional liquidcrystal variable retarder 206 that is commercially available fromMeadowlark, Longmont, Colo., a conventional non-polarizing beam splitter208 that is commercially available from Newport Corp., Irvine, Calif., aconventional diffuser 210 that is commercially available from SpindlerHoyer, Germany, a conventional feedback photodiode 212 that iscommercially available from Hamamatsu Corp., Hamamatsu City, Japan, afeedback amplifier and receiver preamplifier 214 that is commerciallyavailable from Analog Design, San Francisco, Calif., a conventionalfocusing lens 216 that is commercially available from NewportCorporation, Irvine, Calif., a custom integrating sphere 218 that iscommercially available from Labsphere, North Sutton, N.H., made from anapproximately 0.62 inch cube aluminum block, which has a 0.54 inchdiameter spherical section removed from its center, a 4 mm diameter holeat the bottom for the scattered light to enter the sphere, another 4 mmdiameter hole at the top for the light to reach a photodetector, twoholes at opposite sides for the specular light to enter and exit thesphere, the internal surfaces are coated with a reflective surface thatscatter light, e.g. Spectralflect, available from Labsphere, NorthSutton, N.H. The integrating sphere 218 has an input hole that isdesigned to be slightly larger than the laser beam diameter so as not toocclude the beam, the output hole diameter is chosen to be large enoughto allow the beam to exit the sphere and small enough to allow for thedetection of the minimum spatial frequency according to equation (3),the diameter of the holes and the diameter of the sphere are chosen sothat the total surface area of the holes is preferably less than fivepercent of the total surface area of the sphere, although the use of alarger percentage is possible. The integrating sphere 218 preferably hasa baffle extending through its center in the same plane as the incidencelight, the baffle has a circular region at its center which is the samediameter as the hole provided for the scattered photodetector. Thebaffle prevents any first reflection from the disk from reaching thephotodetector without first striking the surface of the integratingsphere. The integrating sphere 218 is preferably miniaturized to keepthe entire optical device small.

One embodiment of the apparatus 200 also includes a conventionalcollimating lens 220 that is commercially available from NewportCorporation, Irvine, Calif., a conventional diffuser 222, that iscommercially available from Spindler Hoyer, Germany, a conventionalspecular photodetector 224A and scattered photodetector 224B that iscommercially available from Hamamatsu Corp., Hamamatsu City, Japan, acustom baffle 226 that is commercially available from Labsphere, NorthSutton, N.H., a liquid crystal variable retarder (LCVR) driver 228, anda conventional computer 240, for example a microcontroller or an IBMpersonal computer, commercially available from IBM Corporation, Armonk,N.Y., having a conventional input/output device 242, a conventionalmemory module 244 having unconventional applications stored therein,e.g., the analysis unit 248, and a conventional processor 246, e.g., aPentium Pro Processor that is commercially available from IntelCorporation, Santa Clara, Calif. It will be apparent to persons skilledin the art that the apparatus 200 is the preferred embodiment of thepresent invention and that alternate designs can be used withoutdeparting from the present invention. The operation of the apparatus 200is now described in greater detail.

A laser diode 202 emits an electromagnetic signal toward the thin filmdisk. In the preferred embodiment the electromagnetic signal is a lightsignal having a wavelength of 780 nanometers (nm) although a widevariety of wavelengths can be used. The angle of propagation of thelight signal can be any angle between zero and ninety degrees. However,in the preferred embodiment the angle need not be substantiallyBrewster's angle for the carbon in the thin film. That is, the angle ofpropagation differs from the Brewster's angle of the carbon by a minimumof two to five degrees, for example, at which angle the change in thereflectivity of the thin film based upon the carbon changessignificantly when compared to the reflectivity at Brewster's angle. Theemitted light passes through the linear polarizer 204. The linearpolarizer 204 improves the linear polarization of the laser lightsignal. The polarized light signal passes through a liquid crystalvariable retarder (LCVR) 206. The LCVR 206 switches the polarization ofthe light between P and S linear polarizations in response to aninstruction received from the LCVR driver 228. The LCVR driver 228 canbe located external to or integral with the computer 240. As describedbelow, P and S linear polarizations enable the apparatus 200 to measurea variety of properties of the thin film 100. A description of oneexample of the LCVR driver is now described with reference to FIG. 3.

FIG. 3 is a more detailed illustration of the LCVR driver 228 accordingto the preferred embodiment of the present invention. The LCVR driver228 includes an amplitude control module 302, a gaussian noise module304, a crystal oscillator 306, and a low pass filter 308. In thepreferred embodiment the crystal oscillator is a 2 kHz square waveoscillator whose fundamental frequency is modulated by five percent in arandom manner by Gaussian noise generated by the gaussian noise module304. The 2 kHz square wave amplitude is controlled in two states by theamplitude control module 302 that receives signals from the computer 240so that the P and the S polarizations are achievable. The output of theoscillator is low pass filtered by the low pass filter 308 having acutoff at approximately 15 kHz before being directed to the liquidcrystal. The random modulation of the square wave helps preventcrosstalk in the apparatus 200 from being synchronous with the datasampling.

The linear polarized signal is received by the non-polarizing beamsplitter 208 that splits the linear polarized signal. A portion of thelinear polarized signal is split and is directed toward a diffuser 210and to a feedback photodetector 212. The output of the feedbackphotodetector 212 is received by a feedback amplifier in the feedbackamplifier and receiver preamplifier 214. FIG. 4 is an illustration ofthe feedback amplification system of the preferred embodiment of thepresent invention. The feedback amplification system of the preferredembodiment includes a negative feedback amplifier 402 that receives theoutput of the feedback photodetector 212. The negative feedbackamplifier 402 outputs a signal to the laser diode that preciselycontrols the intensity of the laser diode 202. In one embodiment of thepresent invention the bandwidth of the feedback loop is limited to 15Hz. This allows stablilization of the laser power between DC and 15 Hz.The bandwidth of the feedback loop is sharply cut off above 15 Hz toprevent power frequencies (60 Hz and its harmonics) from modulating thelaser power. An advantage of the external beam splitter 208 togetherwith the reference photodiode 212 is improved temperature stability. Theimproved temperature stability is achieved since the referencephotodiode 212 is identical to the specular 224A and the scattered 224Bphotodetectors. Any temperature changes in the optical sensitivity ofthe reference photodiode 212 are substantially compensated by similarchanges in the specular 224A and scattered 224B photodetectors.

Laser diodes are well known to have an internal photodiode to monitorthe laser output power. Another embodiment of a feedback control circuitto control the optical intensity is to use such a photodiode, which isinternal to the laser diode. This laser diode feeds back a controlsignal to the circuitry described in FIG. 4 and by doing so keeps theintensity of the laser at a constant value.

Conventional systems, for example those described in Meeks, et al.,Optical Surface Analysis of the Head-Disk-Interface of Thin Film Disks,ASME Transactions on Tribology, Vol. 117, pp. 112-118, (Janurary 1995))describe the use of narrow band pass filters (NBPF) on thephotodetectors in order to minimize interference from external lightsources. The NBPF allows only the specified wavelength to reach thedetector. One drawback of this method is that it requires the laser tobe stable at the specified wavelength. This is difficult as the laserwavelength is affected by temperature change, thus the system has to bethermally stabilized.

To eliminate the effect of external light on the instrument, the entiredevice 200 is enclosed in a light tight container which eliminates thepossibility of external light from reaching the detectors. As a resultthe NBPF can be eliminated from the design. Removing the NBPF greatlyreduces the effect of temperature changes on the signal amplitude. Thisimproves the thermal stability of the system.

Another means to improve the stability of the system is to removeelectronic zero drift by use of a black standard. A black standard is adevice that absorbs any light coming toward it. One version of a blackstandard is a cylindrical cavity with a pointed cone inside thecylinder, with all the internal surfaces coated with a black, lightabsorbing material. This is type of black standard is commerciallyavailable from Labsphere, North Sutton, N.H. The electronics typicallydrift over time due to thermal changes, component age, and otherfactors. The black standard provides a stable zero level reference tomeasure and cancel the drift. Prior to each scan the laser beam isdirected into the black standard, the electronics signals are thenmeasured and the zero level is defined. This results in improvedstability in the long-term drift of the zero levels of the system.

The linearly polarized signal that passes through the non-polarizingbeam splitter 208 is directed toward a focusing lens 216 that focusesthe light signal onto an area of the thin film 100 that is locatedbeneath the integrating sphere 218 (a cross-sectional view of theintegrating sphere is illustrated in FIG. 2). A first portion of thefocused light signal reflects off the thin film 100 toward a collimatinglens 220 and a second portion scatters within the integrating sphere218. A more detailed discussion of the reflecting and scattering of thefocused light signal is now set forth.

FIGS. 5(a)-(c) are illustrations of the reflective and scatteringproperties of P and S polarized radiation according to the preferredembodiment of the present invention. The view of FIGS. 5(a)-(c) are froma reverse-angle view in comparison to the view of FIG. 2. FIG. 5(a)illustrates the reflection of the focused light signal (P polarizedlight) off the thin film 100. As described above, the focused Ppolarized light signal is directed toward the thin film 100 at an angle,e.g., an angle that is not substantially Brewster's angle. Some of thefocused P polarized light signal reflects off the lubricant layer 102.Some of the focused P polarized light signal reflects off the carbonlayer 104 while some of the focused P polarized light is absorbed by thecarbon layer, and some of the P polarized light reflects off themagnetic layer 106. FIG. 5(b) illustrates the reflection of the focusedlight signal (S polarized light) off the thin film 100. As describedabove, the focused S polarized light signal is also directed toward thethin film 100 at an angle that is not substantially Brewster's angle.The reflection of the S polarized light is similar to the reflection ofthe P polarized light described above. Specifically, some of the focusedS polarized light signal reflects off the lubricant layer 102. Some ofthe focused S polarized light signals reflect off the carbon layer 104while some of the focused S polarized light is absorbed by the carbonlayer, and some of the S polarized light reflects off the magnetic layer106.

The reflected (specular) light signals I_(sp) pass through an opening inthe integrating sphere 218 toward an optional collimating lens 220. Thecollimating lens collimates the reflected light signals which enablesthe diffuser 222 and specular photodetector 224A to be positioned at afurther distance from the reflection area on the thin film disk 100 thanwould otherwise be possible. The diffuser spreads the beam in a mannersuch that the position sensitivity of the specular photodetector isreduced. This reduces the sensitivity of the photodetector to motion ofthe optical beam induced by wobble of the disk. The diffuser 222 and thespecular photodetector 224A are positioned at an angle that is slightlyoff the normal (e.g., five degrees) of the reflected light path. Thisgeometry reduces the amount of light signals that are reflected off ofthe diffuser 222 and/or the specular photodetector 224A and propagateback into the integrating sphere which can possibly affect the detectionof scattered light, as described below. That is, the addition of thecollimating lens 220 which collimates the light allows the path lengthto be increased so that the amount of tilt of the specular photodetector224A and the diffuser 222 is minimized. When the amount of tilt of thespecular photodetector 224A and diffuser 222 is reduced, the specularphotodetector will receive a greater portion of the reflected signalsince the amount of the specular signal lost due to a reflection off thediffuser 222 or the specular photodetector 224A is minimal. In thepreferred embodiment, the collimating lens 220 is used for a highresolution (short focal length) design. A lower resolution system(longer focal length lens) generally allows sufficient length betweenthe specular photodiode and the integrating sphere to require only asmall tilt of the specular photodiode. The specular signal must not beallowed to return to the integrating sphere since this corrupts thescattered signal and causes a crosstalk between the scattered andspecular signals. The diameter of the light port in the optic main bodyis kept to a minimum to block most of the light that is reflected by anysurface in the specular detector area toward the integrating sphere. Theport diameters are made just slightly larger than the beam diameteritself. They can be stepped (not continuously tapered) to make it easierto fabricate. The specular photodetector 224A outputs a signalrepresenting the amount of light received to the receiver preamplifiersin the feedback amplifier and receiver preamplifiers board 214. Thereceived light is interpreted using the computer 240 in the mannerdescribed below. The operation of the specular photodetector 224A isdescribed in greater detail below.

FIG. 5(c) illustrates the scattering effect of the S or P polarizedlight signals. When the focused light signal strikes the lubricant layer102, the carbon layer 104, and/or the magnetic layer 106, a portion ofthe light will scatter at angles that are not equal to the angle ofincidence. For simplicity, FIG. 5(c) only illustrates reflection off thelubricant layer 102. The scattered component of the light is measured bythe scattered photodetector 224B attached to the integrating sphere 218.Internal to the integrating sphere 218 is a baffle 226 which does notpermit any first reflection scattered light to reach the scatteredphotodetector 224B. This baffle 218 reduces the measurement of hot spotscaused by a direct reflection from the disk into the scatteredphotodetector 224B. The baffle 218 prevents this by forcing anyreflections from the thin film disk 100 to take two or more reflectionsbefore reaching the scattered photodetector 224B.

As described above, the LCVR 206 allows the polarization to be switchedbetween P and S linear polarizations. The P specular light signalprimarily gives information regarding changes in the thickness, or theabsolute thickness of the carbon layer on the thin film disk. The Sspecular light signal primarily gives information regarding changes inthe lubricant thickness which has been applied to the carbon surface.The scattered light, together with the specular light gives ameasurement of the roughness of the thin film disk surface. The methodfor using the specular and scattered components of the P and S polarizedlight to measure thin film 100 characteristics is described below.

FIG. 6 is a more detailed illustration of a photodetector 224 accordingto the preferred embodiment of the present invention. The photodetectorcan be the specular photodetector 224A or the scattered photodetector224B. The photodetector 224 of the preferred embodiment includes abiased photodiode 602, a transconductance preamplifier 604, a bufferamplifier 606, signal conditioning circuitry 607 (available from AnalogDesign, Inc. in Topanga, Calif.) and a GAGE Applied Sciences, Inc.analog to digital board 608, e.g., model number CS1012/PCI that iscommercially available from GAGE Applied Science, Inc., Montreal,Canada. The biased photoconductor 602 receives a light signal andgenerates a signal reflecting the intensity of the received light. Thebiased photodiode signal is amplified by the transconductancepreamplifier 604 which is transmitted to the buffer amplifier 606.Before being digitized by the analog to digital board the signal passesthrough signal conditioning electronics 607. The signal conditioningelectronics 607 subtracts the DC offset of the signal, passes the signalthrough a variable anti-aliasing filter and provides up to 64 timesmultiplication of the encoder signal from the spindle which rotates thethin film disk 100, in the preferred embodiment. The multiplied encodersignal and the index from the spindle are used as the clock and trigger,respectively for the analog to digital board. After the specular andscattered signals have been conditioned they are passed to the analog todigital board 608 where they are digitized. The digitized signal istransmitted to the computer 240 for analysis. The method for analyzingthe received signals to determine properties of the thin film disk 100is set forth below.

The properties of the entire thin film disk 100 can be measured byfocusing the light signal on all areas of the thin film disk 100. Thiscan be accomplished by precisely moving the thin film disk 100 or bymoving the apparatus 200. In the preferred embodiment the apparatus 200is attached to a very accurate stepper motor (not shown) and theapparatus 200 is stepped over the surface of the thin film disk 100. Oneexample of such a stepper motor is Newport's Mikroprecision stage thatis commercially available from Newport, Irvine, Calif.

FIG. 7 is a flow chart illustrating a method for measuring thin filmproperties according to the preferred embodiment of the presentinvention. In the preferred embodiment a differential technique is usedsuch that reference images of the thin film disk are made at thebeginning of the experiment and the reference images are subtracted fromeach of the subsequent images. The resulting differential images showonly what has changed as a result of interacting with the disk duringthe period of time between the reference and subsequent images. Thereference images are not a requirement to analyze the data but it makesany changes in the disk surface easier to identify and increases thesensitivity to changes. However, in alternate embodiments only a singleset (Ssp, Ssc, Psp, and Psc) of images is measured (at a angle that isnot substantially Brewster's angle for the carbon layer 104, forexample) and lubricant thickness and degradation, carbon wear andsurface roughness is determined.

The apparatus 200 measures 702 reference values of the thin film disk atan angle that is not substantially Brewster's angle (as describedabove). These reference values include the specular and scatteredcomponents of the P and S polarized signals received by the specularphotodetector 224A and the scattered photodetector 224B, respectively.The measurements can be taken in situ or ex situ, as described below.The user then performs 704 an action on the thin film disk 100. Forexample, the thin film disk 100 is subjected to repeated start-stopactions such that a ceramic slider of the read/write head repeatedlycontacts the thin film disk 100. This simulates repeated power on/offcycles of a hard disk drive, for example. This contact can causelubricant depletion, lubricant degradation, and carbon layer wear. Afterthe first iteration of action is performed on the thin film disk 100,e.g. a thousand start/stop simulations, the apparatus measures 706 newvalues of the thin film disk 100. These new values include the specularand scattered components of the P and S polarized signals received bythe specular photodetector 224A and the scattered photodetector 224B,respectively. The signals representing these values are stored in thecomputer memory module 244 and an analysis unit 248 in the memory moduleanalyzes the values in conjunction with the processor 246. The functionsperformed by the analysis unit 248 are described below.

The analysis unit 248 determines 708 differential values by determiningthe difference in values between each reference value and thecorresponding value in the subsequent measurement of the thin film disk100. The differential values include the difference (delta) in thespecular component of the S polarized light (ΔS_(SP)), i.e., thereflectance received by the specular photodetector 224A when S polarizedlight is transmitted toward the thin film disk, the delta in thespecular component of the P polarized light (ΔP_(SP)), the delta in thescattered component of the S polarized light (ΔS_(SC)), and the delta inthe scattered component of the P polarized light (ΔP_(SC)). Thesedifferential values are used to identify thin film properties asdescribed below. One technique for measuring the reflectance of a lasersignal striking the thin film disk 100 at Brewster's angle of the carbonlayer 104 is described in the S. Meeks et. al., Optical Surface Analysisof the Head-Disk-Interface of Thin Film Disks, ASME Transactions onTribology, Vol. 117, pp. 112-118, (Janurary 1995), that was incorporatedby reference above.

The subtraction of the reference and subsequent images is degraded bythe presence of thermal drift during the time between the gathering ofthe reference and subsequent images. This thermal drift is caused by thethermal expansion of the disk and other components with variations inenvironmental temperature. The thermal drift can be corrected byshifting each image with respect to the other in the radial direction ofthe thin film disk. The shifted images are shifted and the crosscorrelation between the two images is computed. The amount of shift isincreased and the cross correlation is repeated until a maximum isreached. The shift at which the maximum in the cross correlation occursis the optimal shift, i.e., the one which corrects for the thermal driftof the components. An alternative to using the cross correlation is tosubtract the images and compute the variance or standard deviationbetween the two images. The shift is then increased and the variance orstandard deviation is again computed. The amount of shift whichminimizes the standard deviation or variance is the optimal shift whichwill correct for the thermal drift.

In order to better understand the method for analyzing the differentialvalues, a description of the effect of the thickness of the lubricantlayer and the thickness of the carbon layer 104 on the amount of lightreceived by the specular photodetector 224A and the scatteredphotodetector 224B is now set forth.

FIG. 8 is a graph illustrating the reflectance of P and S polarizedradiation off a thin film having no lubricant layer 102 and having alubricant layer 102 whose depth is ten nanometers according to thepreferred embodiment of the present invention. FIG. 8 shows thesimulated specular reflectivity of the S and P polarized light versusthe angle of incidence of the light signal on the thin film disk. Inthis example the light signal has a wavelength of 650 nm. Two curves areshown, one with no lubricant applied (black) to the carbon surface andthe other with ten nm of lubricant (white) applied. An unrealisticallythick layer of lubricant has been shown in this figure to illustrate thedifferences between the curves. The difference between the two curvesrepresents the P and S polarized specular light sensitivity tolubricant. At angles between zero degrees and approximately 53 degreesthe reflectivity of the disk decreases when lubricant is added to thedisk for both the P and S polarized light signals. At angles aboveapproximately 53 degrees the reflectivity of the disk decreases for Spolarized light and increases for P polarized light, when lubricant isadded to the carbon surface. At approximately 53 degrees, the Ppolarized light is insensitive to lubricant on the surface, because thisis the Brewster's angle of the lubricant. At angles near 80 degrees theP polarized light reaches a maximum in its sensitivity tolubricant—approximately 2 or 3 times the sensitivity of the S polarizedlight. The angle of 53 degrees is a specific example of the Brewster'sangle of the lubricant which is defined as the Arc Tan of [index ofrefraction of lubricant/index of refraction of air].

The ratio between the P sensitivity to lubricant and the S sensitivitychanges as a function of the angle as can be seen in FIG. 8. At a fixedangle of incidence this ratio is related to the index of refraction ofthe lubricant. Therefore, if the lubricant degrades, the index ofrefraction also changes and the ratio of the change in the specularcomponent of the S polarized light (ΔS_(SP)) to the change in thespecular component of the P polarized light (ΔP_(SP)) will change. Thisis one technique for measuring the degradation of the lubricant on athin film disk 100. The angle of 53 degrees is particularly good forthis since even a very small change in the lubricant index will generatea large change in the ratio of delta S (ΔS_(SP)) to delta P (ΔP_(SP)).

FIG. 9 is a graph illustrating the reflectance of P and S polarizedradiation off a thin film having a carbon layer 104 of twenty nanometersand having a carbon layer of fifteen nanometers according to thepreferred embodiment of the present invention. The black curve shows theS and P reflectivity versus angle of incidence with 20 nm of carbonpresent. The white curve shows the same curves when 5 nm of carbon hasbeen removed. Both the S and P polarization's can be used to measurecarbon wear, but in general P is more sensitive and more linear in itsresponse to wear of the carbon. The S reflectivity increases when carbonis removed at all angles of incidence. The P polarized light increasesfor carbon removal for angles less than approximately 71 degrees, iszero at approximately 71 degrees and decreases when the angle is greaterthan 71 degrees. The maximum sensitivity to carbon thickness or carbonwear occurs near zero degrees. The angle of 71 degrees is a specificexample of the “P polarization crosspoint angle” which is defined as theangle at which the P polarized beam reflection coefficient isinsensitive to the carbon thickness change.

In the preferred embodiment the angle of incidence is 58 degrees tomeasure all lubricant features, carbon thickness and wear and surfaceroughness. However, as described above, many angles can be used.Operation at 58 degrees allows the user to easily separate lubricantthickness increase (P reflectivity increase, S decrease, see FIG. 8)from carbon wear (S and P reflectivity increase). This technique formeasuring carbon wear is not limited to carbon overcoats. The wear ofany absorbing layer can be measured by the embodiments discussed here.In particular, overcoats such as Zirconium Oxide, Silicon Dioxide,organic materials and plastics, for example, can be used. If thesealternative overcoats have lubricant on them, then the lubricantthickness, depletion and degradation may be measured as well.

One technique for identifying the lubricant thickness change from carbonwear based upon ΔS_(SP) and ΔP_(SP) is to use a two-dimensionalconcentration histogram. A technique for generating and using atwo-dimensional concentration histogram is described by S. Meeks et.al., Optical Surface Analysis of the Head-Disk-Interface of Thin FilmDisks, ASME Transactions on Tribology, Vol. 117, pp. 112-118, (Janurary1995), that was incorporated by reference above. To construct a twodimensional histogram small regions (known as buckets) are defined inthe P, S plane (the space of the histogram) which have a certain ΔP byΔS dimension. Each coordinate pair (x,y) in the real space image isselected and its corresponding bucket into which its P, S coordinatefalls is identified. After going through the entire image the totalnumber of points in each bucket is identified and a color, for example,is assigned based upon the number of points in the bucket. The completedtwo dimensional image is known as a two-dimensional concentrationhistogram. The two-dimensional concentration histogram separates theregions of lubricant pooling, depletion, carbon wear and debris intoseparate regions. Debris are products generated as a result of the wearprocess on the disk. In addition, the slope of the histogram is relatedto the index of refraction of the layer being altered. As describedbelow, the slope of the histogram can be used to differentiate betweenlubricant depletion and carbon depletion. Some examples of histogramswhich each corresponds to a different embodiment of the presentinvention are set forth in FIGS. 10-13.

FIG. 10 is a histogram illustrating the relationship between changes inS polarized radiation (ΔS_(SP)) and P polarized radiation (ΔP_(SP)) withrespect to thin film measurements when an angle of incidence of theradiation source is between approximately 53 degrees and approximately71 degrees according to the preferred embodiment of the presentinvention. The angle of 53 degrees is a specific example of theBrewster's angle of the lubricant which is defined as the Arc Tan of(index of refraction of lubricant/index of refraction of air). The angleof 71 degrees is a specific example of the “P polarization crosspointangle” which is defined as the angle at which the P polarized beamreflection coefficient is insensitive to the carbon thickness change.

In the preferred embodiment, the analysis unit 248 identifies 710lubricant pooling or depletion or identifies 712 carbon wear using thedifferential specular values (ΔS_(SP), ΔP_(SP)) in the following manner.When the angle of incidence that the focused light signal strikes thethin film is between approximately 53 degrees and 71 degrees, if thevalue of ΔS_(SP) is positive and the value of ΔP_(SP) is negative thenthe analysis unit 248 determines that thin film disk 100 has experiencedlubricant depletion. Using the histogram illustrated in FIG. 10 this isdetermined by locating the quadrant in which the ΔS_(SP), ΔP_(SP) datais located, in this example, the data is located in quadrant II which isidentified as lubricant depletion. The analysis unit 248 determines theamount of lubricant depletion or pooling based upon the value of ΔS_(SP)and a calibration of the amount of ΔS_(SP) change per angstrom oflubricant change.

This range of angle of incidence allows easy distinction in themeasurements of lubricant pooling/depletion, carbon wear, and debris.The lubricant pooling, depletion, carbon wear, and debris will be indifferent quadrants of the two dimensional histogram, making it easierto separate the data. This data from each of the four quadrants can betraced back to the original images (P and S images in real space)indicating the locations on the disk of lubricant pooling, depletion,carbon wear, and debris.

If both ΔS_(SP) and ΔP_(SP) are positive then the analysis unit 248determines that the thin film disk 100 experienced carbon wear. Theanalysis unit can determine the amount of carbon wear using a variety oftechniques. Some of these techniques are described below. If ΔS_(SP) isnegative and ΔP_(SP) is positive then the analysis unit 248 determinesthat the thin film disk 100 experienced lubricant pooling. As describedabove, the ratio of ΔS_(SP)/ΔP_(SP) correlates to the index ofrefraction of the lubricant. The expected value of this ratio is knownand is stored in the computer memory module 244. If the analysis unit248 determines that the ratio of ΔS_(SP)/ΔP_(SP) does not correspond tothe expected value of this ratio, the analysis unit determines 714 thatlubricant of the lubricant layer degraded.

FIG. 11 is a histogram illustrating the relationship between changes inS polarized radiation (ΔS_(SP)) and P polarized radiation (ΔP_(SP)) withrespect to thin film measurements when an angle of incidence of theradiation source is approximately 53 degrees (in general, Brewster'sangle of the lubricant) according to one embodiment of the presentinvention. This angle of incidence enhances sensitivity to changes inthe lubricant index of refraction. This is an embodiment which isoptimized for measuring lubricant degradation. A change in the lubricantindex of refraction is related to the degradation of the lubricant.

FIG. 12 is a histogram illustrating the relationship between changes inS polarized radiation (ΔS_(SP)) and P polarized radiation (ΔP_(SP)) withrespect to thin film measurements when an angle of incidence of theradiation source is less than 53 degrees according to one embodiment ofthe present invention. This range of angle of incidence enhancessensitivity to lubricant, carbon thickness change and absolute carbonthickness. This embodiment is optimized for measuring lubricantpooling/depletion, carbon wear and carbon thickness.

FIG. 13 is a histogram illustrating the relationship between changes inS polarized radiation (ΔS_(SP)) and P polarized radiation (ΔP_(SP)) withrespect to thin film measurements when an angle of incidence of theradiation source is between 71 degrees and 90 degrees according to thepreferred embodiment of the present invention. This range of angle ofincidence has the highest sensitivity to lubricant thickness change,specifically the P-polarized light. This embodiment is optimized formeasuring lubricant pooling/depletion. When in this range of angles, thespatial frequency of the measured surface roughness is nearly twice aslarge as when measured at near normal incidence. This allows themeasurement of high spatial frequency roughness (microroughness).

The technique used for analyzing these histograms is similar to thedescription set forth above. With respect to FIG. 12, since the valuesof ΔS_(SP) and ΔP_(SP) are both positive for lubricant depletion andcarbon wear, one technique for identifying which occurs is to determinethe point at which the slope of the histogram changes, as illustrated inFIG. 12. The ΔP_(SP), ΔS_(SP) histograms are constructed by subtractingthe reference images (taken before any testing has begun) from datagathered during the testing procedure (start/stops, thin film headflying or dragging). The differential images are constructed asdescribed earlier and the analysis described above is applied to thehistograms. A time sequence of histograms can be constructed bysubtracting images at various time points from the reference images. Inthis manner the evolution of the histograms and hence the disk surfacecan be followed and analyzed.

The analysis unit 248 identifies 716 the surface roughness of the thinfilm disk 100. The roughness is measured simultaneously with themeasurement of the specular light and the scattered light. The analysisunit 248 uses the equation (1) to determine the RMS (root means square)roughness of the thin film disk 100. $\begin{matrix}{{{RMS}\quad {roughness}} = {R_{Q} = \frac{\left\lbrack {({TIS})^{1/2}*\lambda} \right\rbrack}{4*\pi*{\cos (\phi)}}}} & (1)\end{matrix}$

Where λ is the wavelength of the light signal, φ is the angle ofincidence of the light signal, and TIS is the total integrated scatteredportion of the light signal and is defined by equation (2).$\begin{matrix}{{TIS} = \frac{SC}{{SP} + {SC}}} & (2)\end{matrix}$

Where SC is the total scattered light and SP is the total specularlight. As indicated above, the wavelength in the above equation is thewavelength of the incident light. In the preferred embodiment thewavelength is either 780 nm or 650 nm, but in alternate embodiments thewavelength can be any visible or invisible light wavelength. The maximumspatial frequency over which the roughness is measured is determined bythe wavelength of light and the angle of incidence according to equation(3), for example.

f _(g)=(sin ((φ₁)−sin ((φ_(i)))/λ  (3)

Where f_(g) is the maximum spatial frequency, φ₁ is the maximumscattering angle and φ_(i) is the angle of incidence. The minimumspatial frequency is determined by the spot size or the exiting hole ofthe sphere, whichever yields a higher number.

The measurement of the scattered light is used to measure the amount ofcarbon wear and the carbon thickness. The incident intensity is given inequation (4). Equation (4) is simply a statement of the conservation ofenergy.

I _(i) =I _(A)+(I _(SP) +I _(SC))  (4)

Where I_(i) is the incident intensity and I_(A) is the absorbedintensity, which is related to the wear of the carbon film and thethickness of the carbon, I_(SP) is the specularly reflected intensityand I_(SC) is the scattered intensity. The incident intensity is keptfixed and in order to measure the absorbed intensity and hence thecarbon wear or carbon thickness it is necessary to measure both thespecular and scattered light at the given angle of incidence. Thealgorithm for measuring carbon wear can be separated into two cases. Thefirst case is known as an in situ wear measurement described above. FIG.18 shows the flow chart for determining carbon wear for the in situcase. The process includes placing a disk within a test stand and taking1802 reference images at the very beginning of the experiment. Thereference images are the S_(SP), S_(SC) and P_(SP), and P_(SC) imagesbefore anything has been done to the surface of the disk. The disk isthen subjected 1804 to start/stop actions of a thin film magnetic heador any other process which might cause wear of the carbon protectiveovercoat. Intermediate to the start/stops, the disk is scanned 1806numerous times to follow the wear process. At the completion of theexperiment the differential images are constructed 1808 by subtractingthe reference images from the images taken before the start/stop actionsupon the disk. The two dimensional concentration histograms areconstructed by summing ΔP_(SP) and ΔP_(SC) (the difference images formedby subtracting the reference image from the intermediate image) andmaking the two-dimensional concentration histogram with thecorresponding ΔS_(SP) summed with ΔS_(SC). The images can be low passfiltered 1810 and high pass filtered 1811, if necessary and the twodimensional histograms are constructed 1812. The histograms may appearas shown in FIG. 10 and if so the region, which lies in the firstquadrant, corresponds to carbon wear.

The carbon wear can be calibrated 1814 by a curve of P specular lightversus carbon wear such as that shown in FIG. 14. FIG. 14 is atheoretical graph illustrating the change in P reflectivity and theabsolute P reflectivity verses the thickness of a carbon layer in nm.The theoretical curve shown in FIG. 14 has been computed from knowledgeof the complex indices of refraction of the layers of the thin film diskshown in FIG. 1 using a thin film analysis program called “Film Star”that is commercially available from FTG Software Associates, Princeton,N.J. Alternate ways to compute the curves of FIG. 14 are discussed byBorn and Wolf in “Principles of Optics” 6^(th) Edition CambridgeUniversity Press, 1997 beginning at page 51, and by Azzam and Bashara in“Ellipsometry and Polarized Light” North-Holland, 1987 pgs.270-315, forexample. The equations relating reflectivity of a thin film to theabsorbing layer thickness can be found in “Ellipsometry and PolarizedLight” referenced above on pages 283 through 288, for example. Theseequations or similar ones referenced in Born and Wolf may beincorporated into the computer software to automatically predict thefilm thickness from the reflectivity of the disk. In order to predictthe film thickness it is first necessary to know the complex indices ofrefraction of the carbon 104 and magnetic layers 106. The change inreflectivity of the points in the first quadrant of the histogram can berelated to the wear of the carbon through the theoretical change inreflectivity scale (on the right side of FIG. 14) such as the curveillustrated in FIG. 14. The absolute reflectivity scale on the left ofFIG. 14 can be used to compute the absolute thickness of the carbon. Thecomputation of the absolute thickness of the carbon requires knowledgeof the complex indices of refraction of the carbon and magnetic layers.A similar curve can be computed with the S polarized reflectance fromthe thin film disk.

The reflectance on the left and right scales of FIG. 14 are thosemeasured experimentally by the sum of P_(SP) and P_(SC). A system whichuses only the specular component of light will ignore the light whichhas been scattered and will give a measurement of carbon thickness orwear which is incorrect. An additional advantage of using the sum of thespecular and scattered components is that the signal from the carbonwear is essential doubled. This is because as the carbon wears the Pspecular component increases as well as the P scattered component. The Pscattered component increases since most of the P light penetrates theabsorbing film and scatters off the magnetic layer 106. As the carbon isthinned the amount of scattered light from the magnetic layer 106 willincrease, since there is less carbon to absorb the scattered light fromthe magnetic layer.

An alternative method for identifying the amount of carbon wear is tomeasure the k (complex part of the index of refraction) of the carbonand use the percentage reflectivity change per angstrom of carbon wear.FIG. 15 is a graph illustrating the sensitivity of P polarized lightreflectivity to carbon wear verses the k of carbon for a light signalhaving a wavelength of 650 nm and having an angle of incidence of 58degrees. FIG. 15 illustrates the relationship between the sensitivity ofP polarized light to carbon wear versus the imaginary portion of theindex of refraction (k) of the carbon. The initial slope (at200-Angstrom thickness) of the curve in FIG. 14 is similar to theordinate illustrated in FIG. 15 where the changes in the ordinate aredue to the changes in the k of the carbon. The abscissa is the k of thecarbon and the ordinate is the sensitivity of the P specular light tochanges in carbon thickness, expressed in the percentage of P polarizedlight reflectivity change per Angstrom of carbon wear. Typical carbonshave k values near 0.4, making the sensitivity about 0.07 percent perAngstrom of carbon wear. This technique allows the detection of 0.01percent change in the reflectivity and, therefore changes in carbon wearof less than one Angstrom. The graph of FIG. 15 can be used to determinean approximate measure of the carbon wear. The initial slope of thecurve in FIG. 14 is given as the k=0.4 value illustrated in FIG. 15. Thefirst technique, using FIG. 14, has the advantage of accounting for thenonlinearity of the reflectivity change vs. wear. The second technique,using FIG. 15, has the advantage of simplicity. The analysis of thecarbon wear is aided by the use of a one-dimensional wear histogram. Thepixels in the image corresponding to carbon wear (the first quadrant ifthe angle of incidence is 58 degrees) are plotted in a histogram. Thisone-dimensional histogram has as the ordinate the number of pixels andthe abscissa is the amount of carbon wear as calibrated above. Thehistogram allows the user to display the amount of the surface which isworn (the number of pixels) versus the amount of wear. In this mannerthe user can select the amount of wear (a point on the abscissa) anddetermine the percentage of the surface area, which is worn above orbelow this amount of wear. This aids the comparison of different carbonsurfaces in their response to wear induced by the thin film head.

The analysis of the data is accomplished by analyzing the images of thethin film disk as a function of time. The disk is subject to some actionsuch as start/stops of the thin film head, which may alter the disksurface as described above. Images of the disk are repeated at certaintime intervals and these images are analyzed in steps 702-716 via thetwo dimensional histograms. An example of carbon wear analysis using anin situ procedure is shown in FIG. 18. The steps of collecting imagesand analyzing them 702-716 are repeated until the experiment comes to aconclusion. The images are constructed by moving the apparatus 200across a radius of the thin film disk with a very accurate stepper motorwhile rotating the disk at a high rate of speed (1000 to 20000 rpm).

The spindle which rotates the disk at a high rate of speed contains anencoder which produces 1024 pulses as it rotates through 360 degrees,for example. This encoder is used to determine the circumferentialpositions around the disk. The present invention preferably utilizes avery high-resolution determination of the position around thecircumference of the disk. This is accomplished by using a phase lockedloop to multiply the encoder signal by a selectable factor of up to 64times. The phase locked loop, which multiplies the 1024 encoder pulses,has the ability to track any velocity jitter in the encoder. Thisfeature allows averaging of repeated revolutions to be done with no lossof lateral resolution. That is, subsequent revolutions lie in phase withone another and when averaged, the resulting image is not smeared by anyjitter effect. Averaging is done to improve signal-to-noise ratio.

The spectrum of spindle jitter is assumed to be related to the frequencyof spindle rotation, and limited to some multiple of it. Jitter can bedue, for example, to the variations in torque from the motor poles.Regardless of spindle-frequency jitter, the encoder output nonethelessexactly tracks data on the disk. It would be ideal therefore tosynchronize the data-acquisition clock to the encoder. In practice,there are limitations on the frequency at which the clock can be made totrack the encoder. In the phase-locked loop (which generates the clockfor the Analog to digital converter from the encoder) the encoder iscompared to the internal clock reference, generating phase-error pulses.The duty cycle of these pulses constitutes an error signal indicatingwhether the internal reference matches the encoder frequency or shouldbe adjusted to maintain tracking. To convert these pulses to an averagevoltage useful as an error signal requires a low-pass filter, whichlimits the tracking bandwidth. A conflicting parameter is theerror-signal ripple, which diminishes as the low-pass filter cutofffrequency is lowered. Ripple on the error signal leads to smallvariations in the frequency of the multiplied clock. This rise and fallof the clock frequency during each encoder period, while consistent fromscan to scan, and therefore not a threat to averaging could, if large inmagnitude, distort the appearance of data features. The repeatable partof the spindle jitter is not a threat to averaging (although it maydistort the image). The non-repeatable part of the jitter will smear outthe averaged image and this circuit will remove this smearing resultingin high resolution, high signal to noise images.

Since the encoder frequency is 1024 times the spindle frequency,compromise can be struck, placing the cutoff frequency of the low-passfilter at about 50-100 times higher than the spindle frequency, andabout 10-20 times lower than the encoder frequency. In this way, spindlejitter up to >50 times the spindle frequency is tracked, while the clockfrequency remains stable to within±a few percent. Since the encoderfrequency varies widely, the cutoff frequency of the low-pass filtershould be adjusted to maintain the ratios set forth above. The 68:1encoder-frequency range of one embodiment of the present invention isdivided into seven 2:1 ranges, each of which uses a different, fixedfilter configuration set by switching the appropriate capacitor throughan analog multiplexer.

As described above, in the preferred embodiment, the measurement of thethin film disk properties is accomplished in situ. In an alternateembodiment, the measurement of the thin film properties is accomplishedex situ. FIG. 19 is a flow chart illustrating the method for measuringcarbon wear using an ex situ procedure according to the presentinvention. One technique for measuring the thin film disk properties exsitu is to test the thin film magnetic disk on a separate test stand.This means that no reference image needs to be taken. The user placesthe disk on the spindle and the apparatus illustrated in FIG. 2 scansthe disk for carbon wear. This scan provides a measure of the carbonwear, lubricant depletion, lubricant pooling, and surface roughnesschanges at the completion of the experiment. The user measures 1902P_(sp), P_(sc), S_(sp), and S_(sc). The images are high pass filtered1904 to remove any background variations and the DC value of thereflectivity is removed 1906 by setting the average value of the imageto zero. The summed images P_(sp)+P_(sc) and S_(sp)+S_(sc) are thencomputed 1908 and low pass filtered 1910 to remove noise, if necessary.The two dimensional histogram is then computed 1912 and the pointscorresponding to carbon wear are identified. The intensities of thesepoints are related 1914 to the carbon wear in angstroms via such curvesas FIG. 14 and FIG. 15.

The absolute thickness of the carbon may be computed by relating the sumof P_(sp) and P_(sc) or the sum of S_(sp) and S_(sc) via a theoreticalmodel such as shown FIG. 14 to the carbon thickness. This method is notlimited to measuring carbon thickness but can be applied to anyreflective substrate which is coated with an absorbing coating.

Manufacturers make thin film disks with a known carbon overcoatthickness. The control of the carbon thickness is on the order of+/−10%. The knowledge of absolute thickness and the complex indices ofrefraction of the carbon allow one to construct calibration curves suchas FIGS. 14 and 15 and as a result one can determine the amount ofcarbon wear. The change in the thickness of the lubricant can bedetermined from the second or fourth quadrants of the two dimensionalhistogram. The calibration factors for the lubricant are taken from acurve, as described above. The calibration factor will depend at whatangle the particular embodiment is operating. If the embodiment isoperating at an angle between 53 and 71 degrees then the data falling inthe fourth quadrant corresponds to lubricant pooling and in the secondquadrant to lubricant depletion. The absolute thickness of the lubricantcan be determined by removing a section of the lubricant on the disk 100with a suitable solvent. The reflectivity corresponding to the step maybe measured in P or S specular reflectivity. This reflectivity changemay be related to the thickness of the lubricant via curves such as FIG.8. Curves such as FIG. 8 may be computed with software such as “FilmStar” that is commercially available from FTG Software Associates, inPrinceton, N.J. Either S or P reflectivity may be used but Sreflectivity is preferred since the sensitivity to lubricant in Sreflectivity is nearly independent of the k of the carbon when k is lessthan 1.

When the embodiment is operating at an angle between 53 and 71 degreesthe measurement of a step in the lubricant can be enhanced by performingthe ratio of the S image to the P image or vice versa. This gives anenhanced contrast to lubricant for two reasons: 1) the ratio of P to Sor S to P removes most reflectivity variations on the disk and showsonly the step in the lubricant. 2) The response of S light to thelubricant step is opposite to that for P light and as a result the ratioimage increases the signal from the lubricant step. The sensitivity ofthe ratio of the S to P image (or P to S) to lubricant may be calibratedin a manner similar to the S or P specular images are calibrated forlubricant thickness.

Tribologists need to measure how lubricants move on the surface of thinfilm disks 100 since the motion of the lubricant is very important indetermining the durability of the carbon protective layer. The ratio mayalso be used to observe the motion (mobility) of the lubricant. Theratio gives enhanced contrast and removes reflectivity variationsunrelated to the lubricant step, as discussed above. The ratio alsoallows the user to remove the disk with a lubricant step and place themunder some environmental stress (such as humidity or temperature) andthen replace the disk and measure how far the lubricant step has moved.This would not be possible without using the ratio, as the absoluteimages do not have sufficient contrast to pick out the lubricant step.

The ratio of the P to the S images can also be used to identify deep orunusual texture lines on the disk surface. This is possible since theratio of these images is related to the index of refraction of the areabeing sampled by the optical beam. Unusual or deep texture lines haveless carbon on them or contaminates within them. As a result the ratioimage gives a strong contrast to deep or unusual texture lines since thelack of carbon or contaminates changes the index of refraction and as aresult the ratio of P to S or S to P. The ratio of the P to the S imagescan also be used to identify contamination on the disk sincecontamination on the disk will cause the optical properties to change.In particular, the complex index of refraction will be changed by acontaminate beneath or upon the film and the ratio of P to S will showthis as a contrast between various areas of the disk. The individualimages will also show contaminates as changes in reflectivity, howeverthe ratio of P to S or S to P will show the changes more clearly sincethe ratio is constant except for areas where contamination is present.

In addition to measuring the lubricant properties and carbon wear, thepresent invention can simultaneously measure the surface roughness ofthe thin film disk 100 using the technique described above. The image ofthe roughness of the thin film magnetic disk gives the variation of theroughness of the disk with position. The roughness or polish of the diskis typically due to a mechanical polish, which produces polish marks,which are roughly circumferential in nature. By making the Fast FourierTransform (FFT) of the roughness image (obtained from equation 1) or oneof the specular images one can display the spatial frequencies of theroughly circumferential polish in the spatial frequency domain. The FFTcan be used to measure the angular distribution of the polish lines,which is a parameter of interest in the manufacture of thin film disks.The FFT of the roughness image gives the angular distribution of theroughness of the texture lines and the roughness power density of thetexture lines running along a particular direction. FIG. 16 is anillustration of a FFT of a disk texture taken from the roughness imageor one of the specular images as utilized by the preferred embodiment ofthe present invention. A cut through this FFT provides the roughnesspower density of the texture lines verses the angle and the angularwidth of the texture line roughness distribution. FIG. 17 is anillustration of a cut through the fast Fourier transform showing thetexture angles, width and texture power density distribution of a disktexture line pattern.

Another feature of the present invention is a method of automaticallyfocusing the apparatus 200 shown in FIG. 2. Automatic focusing can beaccomplished by placing a laser zone textured disk on the spinstand,which accompanies the instrument. A laser zone textured disk is amagnetic thin film disk which has a series of laser melted protuberancesplaced in a spiral pattern near the inner diameter of the disk. Thelaser-melted protuberances prevent the thin film head from sticking tothe disk when the disk is stopped. A spin stand is a test stand uponwhich the disk is placed which rotates the disk and simulates the actionof a disk drive. The apparatus 200 shown in FIG. 2 is placed over thelaser textured zone of the thin film magnetic disk and the specular andscattered output is observed on an oscilloscope while the focus isadjusted. When the instrument comes to a focus the specular andscattered signals from the laser bumps will reach a maximum value.

The properties of lubricants are sensitive to humidity, therefore it isimportant to measure lubricant property as the humidity changes. Oftenthe instrument 200 will operate in a high humidity environment. Heatedoptics allows operation of this embodiment of the present invention inhigh humidity environment. The optics of the instrument are heated toslightly above the environment temperature so that when used in a humidenvironment water will not condense upon the optics. One technique forheating the optics is to use the heat generated by the electronicswithin the optical enclosure. An alternative technique is to place asmall heater in or near the optical assembly 200.

In an alternate embodiment of the present invention the above opticalsurface analysis apparatus and method are used for rapid measurement ofRMS roughness of laser bumps on thin film disk magnetic media which canbe correlated to laser bump heights. This is useful as a process controlfeedback in the manufacture of laser-bumps on thin film disks. Thepreferred embodiment of the present invention includes a small spot sizescatterometer (3-micron resolution) which allows one to resolve thescattered light from individual laser texture bumps. The RMS roughnessof the individual laser bumps can be determined from the ratio of thescattered to the specularly reflected light as computed from equation(1). The RMS roughness of individually resolved laser bumps is afinction of the height of the laser bumps. Therefore the measurement ofthe RMS roughness of laser texture bumps can be used to monitor theheight and the height distribution of laser texture bumps. Thistechnique has the distinct advantage of being extremely fast (10 MHzdata rate)—orders of magnitude faster than conventional optical ormechanical techniques for determining laser bump height.

In an alternate embodiment of the present invention the above opticalsurface analysis apparatus and method are used to help identify theeffects of burnish or glide head on the lubricant layer 102 and/or thecarbon layer 104. A burnish head is a low flying ceramic slider thatflies near the surface of the disk. In doing so it removes asperitesfrom the surface of the disk. A glide head is a low flying ceramicslider that is equipped with a piezoelectric sensor, in the preferredembodiment. The glide head is flown over the surface of the disk andwhen it encounters an asperity it sends a signal that indicates a defectis present on the disk.

It is typically difficult to observe the effects of a burnish or glidehead on the lubricant layer 102 or the carbon layer 104 since there isno conventional system or method for observing these effects in situ,i.e., while in the process of burnishing or gliding the disk. Oneembodiment of the invention combines the system and method describedabove for measuring thin film disk properties with magnetics, friction,stiction, burnish heads and acoustic emission for glide in the mannerdescribed below. The combination permits inspection of the effects ofburnish and glide on the carbon layer 104, e.g., changes in roughness,texture, and/or carbon layer thickness.

During track following, which is when the thin film slider stays at oneparticular radius of the thin film disk for a prolonged period of time,or during accessing on a thin film disk it is possible for the slider todeplete, pool, or degrade the lubricant layer 102. This embodiment ofthe present invention measures and analyzes these effects while theyoccur. For example, a layer of degraded lubricant can form on the diskas a result of prolonged track following. This embodiment measures thelubricant layer 102 properties by measuring the effect the changes inthe lubricant has on the magnetic signals. The result of changes incarbon thickness are measured by changes in the amplitude of themagnetic signal. In addition, all of the measurements can be made insitu, i.e., without removing the disk from the spindle.

This embodiment of the present invention is a tool for characterizingsurface properties such as roughness, lubricant depletion/pooling,lubricant degradation, surface debris, and carbon wear. It measures andimages the disk surface. There are tools with a spindle and a rotaryactuator that can simulate the action of a disk drive, they are commonlyknown as “spinstands”. It also simulates the wear and tear done by themagnetic head as it contacts the disk surface during starting andstopping of the spindle. In addition, the spinstand can include toolsthat measure other properties of the disk. For example, head to diskstiction/friction, magnetic signal amplitude of the disk, acousticemission from contacts between the head and the disk, and sensors thatdetect and map surface features that protrude above the mean fly-heightof the head.

In one embodiment the above described capabilities are combined, whichenables the data from each tool to be correlated to the measurements ofthe other tools. This allows the user to correlate the data because thevarious measurements can be done simultaneously or sequentially andin-situ. This significantly enhances the usefulness of the tool. Forexample, the mechanism behind the failure of a thin film disk duringspindle start/stop can be better understood. In addition, the evolutionof lubricant degradation/depletion, carbon wear, and surface roughnesschanges can be followed as a finction of the number of spindlestart/stops.

In combining this embodiment of the present invention with thespinstand, the optical component of the invention 200 and the spinstandrotary actuator and magnetic head are in very close vicinity. Theoptical components 200 optimally should not take up more than one halfof the disk area, otherwise it could collide with the spinstand rotaryactuator. The invention 200 has a miniaturized form; in particular theintegrating sphere is miniaturized because it is the closest to therotary actuator, which holds the magnetic head.

Another embodiment of the present invention combines the apparatus andmethod for measuring thin film properties, described above, with highresolution optical or mechanical tools such as an atomic forcemicroscope (AFM) to quickly and easily identify damaged areas on a thinfilm disk. A conventional atomic force microscope, for example modelDI-5000 from Digital Instruments, Santa Barbara, California, is capableof providing a very high resolution image of a surface but has a verysmall detection range (viewing diameter), e.g., approximately 100micrometers. Accordingly, it is extremely difficult to find areas on athin film disk that are damaged using conventional AFMs. However, theapparatus 200 and method described above easily and quickly locatesdamaged areas on a thin film disk 100. As described above, oneembodiment of the present invention identifies thin film disk damage inthe form of carbon wear, surface roughness, lubricant depletion,lubricant pooling, and lubricant degradation, for example. Thisembodiment of the present invention uses the optical analyzer apparatus200 to quickly and inexpensively locate damaged portions of a thin filmdisk 100. The apparatus 200 precisely identifies the damaged locations.The AFM is directed to examine the precisely identified damagedlocations. This embodiment enables the AFM to locate and perform a verydetailed analysis of the damaged portion of the disk. Accordingly, thisembodiment of the present invention enables a user to quickly andinexpensively locate one or more damaged portions on a thin film disk100 and enables the user to direct an AFM directly onto the damagedportions much more quickly than is possible using conventional systemsand methods.

A specific example is the study of carbon wear on laser bumps, it isdesirable to be able to find specific laser bumps (from hundreds ofthousands of laser bumps) which have carbon wear. It is preferable tolocate these worn bumps quickly and to study these laser bumps under ahigh power and high resolution measurement or imaging tool. The presentinvention is able to locate the laser bumps quickly but it does not havethe resolution for studying the laser bumps in extreme detail.Conversely, high resolution tools, such as an Atomic Force Microscope(AFM) are too slow to analyze large number of bumps. A combination ofthe two types of tools provides the advantages of both tools. Laserbumps of interest (with carbon wear) can be found quickly using thepresent invention, the position encoder of the spindle holding the diskcan track their locations. The same spindle can also calibrate therelative location of the optical beam position to the location of theAFM. These laser bumps can then be placed under the high-resolution tool(e.g. AFM) for further study.

Another embodiment of the present invention is a system and method forperforming high temperature film measurement. FIG. 20 is an illustrationof a high temperature thin film measurement system 2000 according to oneembodiment of the present invention. The high temperature system 2000 isa reverse angle illustration when compared to the view illustrated inFIG. 2. The system 2000 is capable of measuring the carbon filmthickness and wear, lubricant film thickness and thickness variation,surface roughness, and degradation of lubricant. The system design issimilar to design set forth above with respect to FIG. 2, for example.One variation is that the high temperature thin film measurement system2000 allows operation at high temperatures, e.g., 80 degrees Celsius.The high temperature thin film measurement system 2000 uses a zero ordertemperature compensated quartz half wave plate 2004 available from, forexample, CVI Laser, Albuquerque, N. Mex. and a high temperature laserdiode 2002 available from, for example Rohm Co., LTD. Kyoto, Japan. Thezero order quartz half-wave plate 2004 is mounted in a rotatable housingthat can be rotated through 45 degrees by a miniature motor, for exampleMaxon Precision Motors, Burlingame, Calif. model No. 118426 using gears2008 that are commercially available from W. M. Berg, East Rockaway,N.Y. Rotating the half wave plate through 45 degrees will rotate thepolarization by 90 degrees. The high temperature thin film measurementsystem 2000 also includes an integrating sphere 218 and baffle 226 thatcan be similar to those described above with reference to FIG. 2. Theintegrating sphere 218 is cut out of the interior of a cubic aluminumblock. The high temperature thin film measurement system 2000 alsoincludes a focusing lens 216 and a collimating lens 220 similar to FIG.2. The high temperature thin film measurement system 2000 also includesfeedback circuitry substantially identical to that described in FIG. 4for controlling laser intensity, and amplifying, signal conditioning anddigitizing electronics substantially identical to that described in FIG.6.

One problem to be solved is to develop a high temperature filmmeasurement system. Hard disk drive and disk manufacturers need to testthe carbon and lubricant on their disks at relatively high temperatures,e.g., 80 degrees Celsius. This can be accomplished by making a filmmeasurement system which can be operated at these temperatures. Themeans to accomplish this is to use a mechanically rotatable temperaturecompensated zero order half wave plate 2004 together with a hightemperature laser diode 2002. The laser which is used is available fromRohm Co., LTD. In Kyoto, Japan and the model number is RLD-78MAT1. Thisis a 780 nm laser diode which has low noise and can operate continuouslyat 80 degrees C. The temperature compensated zero order half wave plateis available from CVI Laser Corp. in Albuquerque, N. Mex., U.S.A. Allthe other optical and electrical components are rated at temperatureshigher than 80 degrees C., so the resulting system can be operated up to80 degrees C. and it may be operated at a humidity of 80% RH (relativehumidity).

Disk drive companies and their suppliers test the thin film disks andthe completed disk drives in environments of up to 70 degrees C. at arelative humidity of 80%, for example. Conventional systems use a laserwhich is either Peltier cooled or an uncooled intensity stabilizedlaser. The Peltier cooled laser suffers from several problems, namely,when attempting to use a cooled laser (cooled for example to 25 degreesC.) in a chamber at a temperature of 70 degrees C. and a relativehumidity of 80%, water will condense on the cooled surface of the laserthus damaging the optical surface. Attempts to operate the Peltiercooler at a temperature of greater than 50 or 60 degrees C. can damage aconventional laser. The embodiment shown in FIG. 20 uses an uncooledlaser 2002 that has been developed for continuous operation at atemperature of 80 degrees C. The system described in FIG. 20 will alsowork at a relative humidity of 80% since the laser actually operates ata temperature slightly greater than its ambient surroundings.

Another problem which needs to be overcome in high temperature systemsis a means to switch the polarization between the P and S polarizations.Conventional liquid crystal variable half wave plates 206 cannot beoperated above 50 degrees C. A solution to this problem is to use a zeroorder thermally compensated half-wave plate. The type of wave plate hasa thermal compensation which allows it to operate to temperaturesgreater than 80 degrees C. The zero-order half wave plate ismechanically rotated in order to switch the polarization between the Pand S states. This is accomplished by a miniature electric motor 2006and gears 2008. In order to reduce the effect of temperature on theelectronics the preamplifier and laser regulator board 214 are locatedoutside the high temperature environment. The connections between thephotodetectors and the board 214 are made with cables.

The system shown in FIG. 20 operates in a manner similar to that shownin FIG. 2. This system has a input aperture 2016 in the integratingsphere 218 which is slightly larger than the optical beam so that thebeam is not eclipsed by the opening. The integrating sphere 218 has ahole 2022 in its bottom that allows the beam to strike the disk andreflect out of the integrating sphere through an aperture 2024. Aperture2024 is slightly larger than the beam to allow the beam to pass throughwithout being eclipsed. The location of aperture 2024 is less than 1 cmfrom the surface of the disk. The diameter of aperture 2024 can controlthe minimum spatial frequency of roughness, which the device can measureaccording to equation (3), discussed supra. The integrating sphereincludes an opening at its top 2018 to allow scattered light to strikethe scattered photodetector 224B. The specular beam is directed onto acollimating lens 220 which prevents the beam from spreading. Afterpassing through the collimating lens it passes into a miniatureintegrating sphere 2028 through an opening 2030. The integrating spherereduces the sensitivity of the photodetector to disk distortion andrunout. A distorted disk is one which differs from a perfect flat plane.The manufacturing process or the process of clamping the disk on thespindle can cause distortion of a disk. Disk runout is the motion of thedisk in the vertical direction caused by imperfection in the spindle andmechanical vibrations of the disk. The specular intensity is detectedvia a hole 2032 in the miniature integrating sphere with a specularphotodetector 224A. The hole 2030 is designed to be larger than thecollimated specular beam so that the beam is not eclipsed by the beam.The integrating sphere 2028 is rotated slightly in the plane of thepaper so that its entrance port is not perpendicular to the beam. Thismeans that the reflected signal from the back of the integrating sphere2028 will not retro-reflect down the optical path into the scatteredlight integrating sphere 218. Retro-reflect means to reflectsubstantially directly down the path of the incoming laser beam. Theamount of reflected light which gets into the integrating sphere 218 isfurther reduced by using an opaque black baffle 2026 placed between theintegrating sphere 218 and the collimating lens 220. Another means ofreducing the sensitivity of the specular photodetector 224A to diskdistortion is to place a diffuser 222 in front of the specularphotodetector 224A as shown in FIG. 2.

An optical surface analyzer, for example the apparatus 200, 2000described above, measures thickness changes induced by wear of multiplelayers of thin film coating on a reflective surface, e.g. magnetic diskmedia. Another feature of the present invention is a system and methodfor separating and identifying the signals from the different layers ofthe thin film using a 2-D histogram. This method is described in detailby Steven Meeks, W. Weresin, and H. Rosen in ASME Journal of Tribology,vol. 117, pg. 112, published in Janurary 1995 which was incorporated byreference above.

The 2-D histogram is generated by the instrument software and allows theuser to select specific areas of interest in the histogram, such as thecarbon wear signal, by manually tracing a line around that area. Thesoftware then finds and highlights the location of the selected area ofthe histogram on the image of the disk by tracing back to the imagesource location. To construct a two dimensional histogram small regions(known as buckets) are defined in the P, S plane (the space of thehistogram) which have a certain ΔP by ΔS dimension. Each coordinate pair(x,y) in the real space image is selected and its corresponding bucketinto which its P, S coordinate falls is identified. After going throughthe entire image the total number of points in each bucket is identifiedand a color, for example, is assigned based upon the number of points inthe bucket. The completed two dimensional image is known as atwo-dimensional concentration histogram. The two-dimensionalconcentration histogram separates the regions of lubricant pooling,depletion, carbon wear and debris into separate regions. Debris areproducts generated as a result of the wear process on the disk. Inaddition, the slope of the histogram is related to the index ofrefraction of the layer being altered. One technique for generating atwo-dimensional histograms is also discussed in detail by Bright andMarinenko, in Microscopy: The Key Research Tool, Vol. 22 pg. 21, 1992 inan article entitled “Concentration Histogram Imaging: A QuantitativeView of Related Images”.

Three embodiments of the present invention each use a method forautomatically selecting specific areas of interest, such as the carbonwear signal, degraded lube, lubricant pooling/depletion, debris anddefects without operator intervention and then using this information tooptimize the type of carbon or lubricant or to analyze the failure of adisk drive.

The three methods are: (1) performing a symmetry operation about acentroid, (2) subtracting a reference histogram and (3) performing anand/not operation with a reference histogram.

The three embodiments can be performed in a conventional computersystem, e.g., a personal computer, a microcontroller, a single chipcomputer, a network. As an example, these embodiments of presentinvention can be performed on a conventional computer system, e.g., aconventional personal computer, or a microcontroller for example, suchas that illustrated in FIG. 21. The computer system illustrated in FIG.21 includes a conventional processor, such as a Pentium II 400 MHzprocessor, a conventional storage unit 2104, a conventional I/O unit2106 and conventional memory 2108. In one embodiment of the presentinvention the memory 2108 can include software related to the operatingsystem 2110, e.g., Windows 98 that is commercially available fromMicrosoft Corporation, Redmond, Wash. In addition, some embodiments ofthe present invention can include one or more of the symmetry unit 2112,the histogram subtraction unit 2114, and the AND/NOT unit 2116. A moredetailed description of the symmetry unit 2112, the histogramsubtraction unit 2114, and the AND/NOT unit 2116 is set forth below.

One embodiment of the present invention is to have the symmetry unit2112 perform a symmetry operation about the centroid of the histogram tocreate a symmetric histogram about the centroid. FIG. 22 is a flowchartillustrating the operation of the symmetry unit 2112 according to oneembodiment of the present invention. The symmetry unit 2112 receives2202 the histogram. The two-dimensional histogram can be created in themanner described above. The symmetry unit 2112 determines 2204 thecentroid of the histogram. One technique for identifying the centroid ofa 2D Histogram is now set forth. The symmetry unit first converts the 2Dhistogram into a binary representation, e.g., any non-zero pixel valuesbecome “1”′ otherwise the pixel takes the value of “0”. Second, fromthis binary image, a skeletonization/Medial Axis transformation inperformed. Skeletonization is a process for reducing a binary image into a skeletal remnant that largely preserves the extent and connectivityof the original region. Skeletonization is one of the morphologicalfilters for Digital Image Processing. Further processing (e.g., pruningby thinning or erosion) may be necessary to produce a skeleton that isfree of spurious spurs which can be introduced during the process ofskeletonization. Next, other morphological filters can be used inaddition to or separately from ‘skeletonization’ to get betterrepresentation of the centriod, such filters include: thinning, which isessentially reducing a binary image shape into a single pixel thickness,and erosion, which is a process to erode away the boundaries of theoriginal region. This operation can remove speckle noise on the 2Dhistogram image, for example. One example of the skeletonization processis described in detail in ‘Digital Imaging’ by Howard E. Burdick,McGraw-Hill, 1997 which is incorporated by reference herein in itsentirety.

The symmetry unit 2112 mirrors 2206 the left side of the histogram aboutthe centroid line onto the right side and subtracts 2208 the mirroredleft side from the right side of the histogram. The resulting histogramrepresents the asymmetric portions of the histogram which can beidentified via a look up table as containing carbon wear, debris,defects, etc. Once the areas of interest are identified, parameters suchas percent of surface area covered by wear, depth of wear, degradedlube, etc., can be calculated automatically.

FIG. 25 is an example of a simplified two-dimensional histogram imageaccording to an embodiment of the present invention. The signal from thethin-film thickness change (e.g. carbon wear) is shown as the shadedarea 2502. The goal is to remove the non-shaded portion of the histogramfrom the data. This area can be automatically isolated from the rest ofthe image by calculating the centroid line 2504 that is a closeapproximation of the line of symmetry of the non-shaded area. The region2506 of the histogram which is symmetric about the centroid line 2504 ofthe histogram image can then be removed from the data. In this example,the data to the left of the centroid line 2504 and its symmetric part onthe opposite side of the centroid line 2504 is to be subtracted 2208from the histogram. What remains is the shaded area 2502 which is thesignal from the worn area. This area corresponding to carbon wear can beprojected on to the P_(sum) axis and with proper calibration they cangive a quantitative amount of the carbon wear. The same calibrationfactors discussed earlier in this text may be used to compute the amountof carbon wear. This technique lends itself to the automatic analysis ofdata. For example, the automatic analysis of the percent of the surfaceworn and a 1D histogram of the wear of the carbon.

The 2D histogram consists of values at (x, y) bin positions whoseamplitude is given by counting the number of points from two spatiallyidentical images of amplitudes x and y which fall within the binpositions. Bin positions are the locations of small areas of dimensionsΔx by Δy whose purpose is to serve as buckets which can accumulate andcount the number of points which fall into these dimensions at aspecified location. The 2D histogram may be formed by any two imagesmeasured over the same spatial location.

The analysis of the portions of the histogram which remain after thesubtraction of the symmetric part of the histogram can be analyzed basedupon the values of the P_(sum) and S_(sum). FIG. 26 is a chartillustrating an analysis technique according to one embodiment of thepresent invention.

If the Psum/Ssum are both positive, i.e., the values fall into quadrant1, the tested area of the disk has only carbon wear. If the values fallinto quadrant 2 then the tested area of the disk has lubricantdepletion. If the values fall into quadrant 3 then the tested area ofthe disk has degraded lubricant and/or debris, or unusual texture lines.If the values fall into quadrant 4 the tested area of the disk has mixedcarbon wear and degraded lubricant or lubricant pooling or organicpooling.

Another embodiment of the present invention uses a reference histogramwhich is subtracted from the histogram of the disk to be measured. FIG.23 is a flow chart illustrating the operation of the histogramsubtraction unit 2114 according to one embodiment of the presentinvention. The histogram subtraction unit 2114 receives 2304 a first(reference) histogram that can represent measurements from a thin filmdisk which is very similar to the disk to be measured but has no damageon its surface. For example, the first histogram can be the histogram ofthe disk before testing, or a disk from the same batch (a sister disk)or the histogram from the untested side of the disk to be measured, forexample.

If a reference histogram is not available from a sister disk, areference histogram can also be obtained in one of several ways. Thefirst way is to construct a 2D histogram from a subset of the currentimage (the surface under test). The subset is chosen on a region of thedisk under test which has no damage, so that it provides a histogram ofa virgin surface. Alternatively, a representation of the background (thereference histogram) can be obtained by performing a ‘traceforward’operation on an undamaged region of the image that makes up the 2DHistogram of the disk under test. The ‘traceforward’ operation isperformed on a subset of the image that is deemed to be free of defectsor damage. The ‘traceforward’ operation is described in detail by Brightand Marinenko, in Microscopy: The Key Research Tool, Vol. 22 pg. 21,1992 in an article entitled “Concentration Histogram Imaging: AQuantitative View of Related Images”. The resulting collection of pixelswhich is now in the 2d histogram domain can be used as representativepixels of a background histogram for that particular image.

One technique for calculating the traceforward is to (1) first obtainthe region on the original image where the traceforward is desired, and(2) for each pixel inside the region selected for the traceforward onthe original images that form the 2D histogram a location in the 2Dhistogram can be calculated from the pixel value of the first imagesource and the second image source. The pixel values will fall into aparticular x-axis bin and y-axis bin respectively, on the 2D histogram.

The histogram subtraction unit 2114 also receives 2304 a secondhistogram representing the disk after testing, for example. Thehistogram subtraction unit 2114 determines 2306 whether all points havebeen selected from each histogram. If not, the histogram subtractionunit 2114 selects 2308 a point in each histogram, e.g., A[x,y] andB[x,y]. The histogram subtraction unit 2114 then generates a resultinghistogram (R) by subtracting 2310 the point from the histogram undertest, B[x,y], from the reference histogram point, A[x,y], (or vice versawith the appropriate modification to the analysis using FIG. 26). Theresulting histogram is separated into the four separate quadrants asdescribed above with reference to FIG. 26.

Another embodiment of the present invention uses a reference histogramwhich a NOT operation is performed between a reference histogram and adata histogram followed by an AND operation. FIG. 24 is a flow chartillustrating the operation of the AND/NOT unit 2116 according to oneembodiment of the present invention. The AND/NOT unit 2116 receives 2402two histograms, e.g., a reference histogram (B) and a data or testhistogram (A), as described above. The AND/NOT unit 2116 selects 2404 apoint (x,y) in each histogram. If the value of the selected point in thereference histogram is greater than zero then the AND/NOT unit 2116 sets2408 the corresponding point in the resulting histogram equal to zero.If the value of the selected point in the reference histogram is notgreater than zero then the AND/NOT unit 2116 sets the point in theresulting histogram equal to the selected point in the test histogram,i.e., R[x,y]=A[x,y].

The AND/NOT unit 2116 uses a reference histogram in which an ANDoperation is performed between the reference histogram and the datahistogram followed by a NOT operation. This yields a resultant histogramwhich contains only those regions which are not common to both the dataand reference histograms.

The resulting and/not histogram is then segmented as shown above andeach quadrant is labeled with the above interpretation. FIG. 27illustrates one example of histogram analysis according to the AND/NOTunit of the present invention. The data from each histogram quadrant canbe traced back to the original data image. The amount of surface areacovered in the original images by each of the regions shown in FIG. 27can be computed and displayed. For example, the total amount of thesurface which has carbon wear can be computed from the traceback. Thedepth of the carbon wear can be computed by calibrating the amount ofcarbon wear corresponding to the reflectivity change.

The above described process can be applied to theP_(sum)=P_(scattered)+P_(specular) Vs S_(sum)=S_(scattered)+S_(specular)histogram or any of the components: P_(scattered), P_(specular),S_(scattered), S_(specular) in any combination versus any othercombination. The reference histogram may be computed from an untestedsister disk, the opposite side of the tested disk, a sub-image histogramcomputed from an undamaged area of the disk under test or from atraceforward computed on an undamaged area of the disk under test, asdiscussed above.

For example, FIG. 28 illustrates one example of histogram analysis usingP specular or S specular versus P scattered or S scattered variableaccording to the AND/NOT unit of the present invention. In this case thefinger 2802 extending into the second quadrant corresponds to corrosionproducts on the disk surface. The slope of the centroid 2804 of thisfinger 2802 is related to the index of refraction of the corrosionproducts. Since different materials have a different index of refractionand hence a different slope, this allows the user to separate debris,corrosion products and texture lines. The second area 2806 along thehorizontal axis of FIG. 28 is the region which has been removed via theAND/NOT operation. The amount of the surface covered by debris ortexture lines is easily computed by calculating the number of pixelscontained in the finger area 2802 of quadrant 2. The finger 2808corresponds to debris on the disk. The slope of the centroid 2810 ofthis finger 2808 is related to the index of refraction of the debris onthe disk surface. This allows the user to quantitatively separate andidentify (from the slope of the centroid) the different particles andcorrosion products on the disk. A substantially identically analysis maybe computed from a 2-dimensional histogram of the P specular versus theS specular light. In this case the two fingers 2802 and 2808 will beextending into the third quadrant. The two fingers will still beseparated by a different slope in a manner substantially identical toFIG. 28.

The above discussion is relating to an instrument, which has an angle ofincidence that is near 60 degrees from the vertical. Similar ideas canbe applied to a machine operating at angles less than or greater than 60degrees. When the angle of incidence changes the interpretation of thevarious quadrants of the histogram will change according to thediscussion given earlier.

While the invention has been particularly shown and described withreference to a preferred embodiment and several alternate embodiments,it will be understood by persons skilled in the relevant art thatvarious changes in form and details can be made therein withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A method for measuring one of a lubricantthickness and lubricant degradation on a thin film disk in a hightemperature environment, the thin film disk having an absorbing layer,and for measuring a roughness of said thin film disk, comprising thesteps of: (a) transmitting a light signal toward a selected location ofthe disk at a first angle using a high temperature laser diode, saidfirst angle at an angle between zero degrees from vertical and ninetydegrees from vertical but not at substantially Brewster's angle of theabsorbing layer; (b) selectively polarizing said light signal using atemperature compensated quartz half plate, said polarization one of a Plinear polarization, an S linear polarization, and a combination of saidP linear and S linear polarizations; (c) said polarized light signalimpinging upon the disk causing a specular component of the polarizedlight signal to be reflected off of the disk at substantially said firstangle and causing a scattered component of said polarized light signal;(d) receiving said specular component from said selected location; (e)collecting said scattered component in a collector positionedsubstantially adjacent to said thin film disk; (f) receiving saidscattered component collected in said collector; (g) determining one ofthe lubricant thickness and lubricant degradation based upon thespecular component of said polarized light signal; and (h) determiningthe surface roughness of said thin film disk based upon said collectedscattered component and said specular component.
 2. The method of claim1, wherein the temperature of the environment is greater than sixtydegrees Celsius.
 3. The method of claim 1, wherein the temperature ofthe environment is greater than seventy degrees Celsius.
 4. The methodof claim 1, wherein the temperature of the environment is greater thanfifty degrees Celsius.
 5. The method of claim 4 further comprising:determining a thickness of the absorbing layer based upon said specularcomponent and said scattered component of said polarized light signal.6. The method of claim 5, wherein said absorbing layer is comprised ofcarbon.
 7. The method of claim 4, wherein said scattered componentincludes only those scattered components that have reflected at leastonce in the collector.
 8. The method of claim 4, further comprising thestep of: (i) identifying a plurality of locations on said thin film diskas the selected position; and (j) repeating steps (a) through (h) foreach of said selected positions.
 9. The method of claim 8, furthercomprising the step of: comparing said specular components and saidscattered components received for a plurality of said selected locationsto identify variations in one of lubricant thickness, lubricantdegradation and roughness in the disk.
 10. The method of claim 8,further comprising the step of: (k) storing first data relating to oneof the lubricant thickness, lubricant degradation, and the roughness ofthe disk at each of said selected positions at a first time; (l)repeating steps (a) through (j) at a second time; and (m) storing seconddata relating to one of the lubricant thickness, lubricant degradation,and the roughness of said thin film at each of said selected positionsat a second time.
 11. The method of claim 10, further comprising thestep of: comparing said first data with said second data to identify oneof a change in lubricant thickness from said first time to said secondtime, a change in lubricant degradation from said first time to saidsecond time, and a change in the roughness of said thin film from saidfirst time to said second time.
 12. The method of claim 11, wherein saidcomparing step includes the steps of: identifying a first change valuerepresenting a change in said specular component of said S linearpolarized light signal between said first time and said second time fora plurality of said selected positions; identifying a second changevalue representing a change in said specular component of said P linearpolarized light signal between said first time and said second time fora plurality of said selected positions; and identifying when one of achange in lubricant thickness, lubricant degradation, and a change inthe roughness of said thin film occurs between said first and secondtime based upon said first change value, said second change value, andthe first angle.
 13. The method of claim 12, where said step ofidentifying when one of a change in lubricant thickness, lubricantdegradation, and a change in the roughness of said thin film occursincludes the steps of: generating a concentration histogram includingsaid first change value and said second change value for a plurality ofsaid selected positions; and identifying one of said change of lubricantthickness and said change in lubricant degradation based upon saidconcentration histogram and the first angle.
 14. The method of claim 13wherein said method is performed in-situ.
 15. The method of claim 12,further comprising the steps of: identifying a first damage locationhaving significant surface roughness; and analyzing said first damagelocation using a high resolution tool.
 16. The method of claim 15,wherein said high resolution tool is one of an atomic force microscopeand an optical microscope.
 17. The method of claim 4, wherein said lightsignal is collimated.
 18. The method of claim 4, further comprising thestep of: focusing said light signal onto said selected location.
 19. Themethod of claim 4, further comprising the step of: focusing saidpolarized light signal onto said selected location.
 20. The method ofclaim 4, wherein said thin film disk is a silicon wafer.
 21. A methodfor measuring an absorbing layer thickness on a thin film disk and formeasuring a roughness of said thin film disk in a high temperatureenvironment comprising the steps of: (a) transmitting a light signaltoward a selected location of the disk at a first angle using a hightemperature laser diode, said first angle at an angle between verticaland ninety degrees from vertical but not at substantially Brewster'sangle of the absorbing layer; (b) selectively polarizing said lightsignal using a temperature compensated quartz half plate, saidpolarization one of a P linear polarization an S linear polarization,and a combination of said P linear and S linear polarizations; (c) saidpolarized light signal impinging upon the disk causing a specularcomponent of the polarized light signal to be reflected off of the diskat substantially said first angle and causing a scattered component ofsaid polarized light signal; (d) receiving said specular component fromsaid selected location; (e) collecting said scattered component in acollector positioned substantially adjacent to said thin film disk; (f)receiving said scattered component collected in said collector; and (g)determining the surface roughness of said thin film disk based upon saidcollected scattered component and said specular component.
 22. Themethod of claim 21, wherein the temperature of the environment isgreater than sixty degrees Celsius.
 23. The method of claim 21, whereinthe temperature of the environment is greater than seventy degreesCelsius.
 24. The method of claim 21, wherein the temperature of theenvironment is greater than fifty degrees Celsius.
 25. The method ofclaim 24, wherein said scattered component includes only those scatteredcomponents that have reflected at least once in the collector.
 26. Themethod of claim 24, further comprising: (h) determining the absorbinglayer thickness based upon said specular component.
 27. The method ofclaim 26, wherein said absorbing layer is comprised of carbon.
 28. Themethod of claim 26, further comprising the step of: (i) identifying aplurality of locations on said thin film disk as the selected position;and (j) repeating steps (a) through (h) for each of said selectedpositions.
 29. The method of claim 28, further comprising the step of:comparing one of said specular components and said scattered componentsreceived for a plurality of said selected locations to identifyvariations in the absorbing layer thickness and the roughness.
 30. Themethod of claim 28, further comprising the step of: (k) storing firstdata relating to the absorbing layer thickness and the roughness of saidthin film at each of said selected positions at a first time; (l)repeating steps (a) through (j) at a second time; and (m) storing seconddata relating to the absorbing layer thickness and the roughness of saidthin film at each of said selected positions at a second time.
 31. Themethod of claim 30, further comprising the step of: comparing said firstdata with said second date to identify one of a change in absorbinglayer thickness from said first time to said second time and a change inthe roughness from said first time to said second time.
 32. The methodof claim 31, wherein said comparing step includes the steps of:identifying a first change value representing a change in said specularcomponent of said S linear polarized light signal between said firsttime and said second time for a plurality of said selected positions;identifying a second change value representing a change in said specularcomponent of said P linear polarized light signal between said firsttime and said second time for a plurality of said selected positions;and identifying when one of a change in absorbing layer thickness and achange in the roughness of said thin film occurs between said first andsecond time based upon said first change value, said second changevalue, and the first angle.
 33. The method of claim 32, where said stepof identifying when one of a change in absorbing layer thickness and achange in the roughness of said thin film occurs includes the steps of:generating a concentration histogram including said first change valueand said second change value for a plurality of said selected positions;and identifying said change of absorbing layer thickness based upon saidconcentration histogram and the first angle.
 34. The method of claim 33wherein said concentration histogram identifies regions of said thinfilm disk having one of lubricant pooling, lubricant depletion,absorbing layer wear, and debris.
 35. The method of claim 34 whereinsaid method is performed in-situ.
 36. The method of claim 33, furthercomprising the steps of: identifying a first damage location havingsignificant surface roughness; and analyzing said first damage locationusing a high resolution tool.
 37. The method of claim 36, wherein saidhigh resolution tool is one of an atomic force microscope and an opticalmicroscope.
 38. The method of claim 24, wherein said light signal iscollimated.
 39. The method of claim 24, further comprising the step of:focusing said light signal onto said selected location.
 40. The methodof claim 24, further comprising the step of: focusing said polarizedlight signal onto said selected location.
 41. The method of claim 24,wherein said thin film disk is a silicon wafer.
 42. An apparatus formeasuring one of lubricant thickness, absorbing layer thickness, andsurface roughness of a thin film disk, said thin film disk having areflective layer in a high temperature environment, the absorbing layersubstantially covering the reflective layer, the lubricant substantiallycovering said absorbing layer, the apparatus comprising: a diskreceiver, for receiving the thin film disk; a high temperature laserdiode, for transmitting a light signal toward a selected location of thethin film disk at a first angle relative to the thin film disk, saidfirst angle at an angle between vertical and ninety degrees fromvertical but not at substantially Brewster's angle of the absorbinglayer, said laser diode capable of operating at high temperatures; atemperature compensated quartz half plate, disposed to receive saidlight signal, for selectively polarizing said light signal to generate apolarized light signal having one of a P linear polarization, an Slinear polarization, and a combination of said P linear and S linearpolarizations, said polarized light signal reflecting off said selectedlocation to generate a specular component and a scattered component,said temperature compensated quartz half plate capable of operating athigh temperatures; a collector, positioned adjacent to said selectedlocation, for collecting said scattered component, said collector havinga first opening for receiving said polarized light signal, a secondopening positioned above said selected location for enabling saidpolarized light signal to strike said selected location, a third openingfor enabling said specular component to exit said collector, and afourth opening; a scattered photodetector, positioned at said fourthopening, for detecting said scattered component; and a specularphotodetector, for detecting said specular component.
 43. The apparatusof claim 42, wherein the temperature of the environment is greater thansixty degrees Celsius.
 44. The apparatus of claim 42, wherein thetemperature of the environment is greater than seventy degrees Celsius.45. The apparatus of claim 42, wherein the temperature of theenvironment is greater than fifty degrees Celsius.
 46. The apparatus ofclaim 45, further comprising: a lens for focusing said polarized lightsignal on said selected location.
 47. The apparatus of claim 45 furthercomprising: a processor; a storage device, disposed to store signalsreceived from said scattered photodetector and said specularphotodetector; and an analysis unit for determining one of lubricantthickness, absorbing layer thickness, and surface roughness of the thinfilm disk based upon said signals stored in said storage device fromsaid scattered photodetector and said specular photodetector.
 48. Theapparatus of claim 47, wherein said analysis unit compares said storedsignals representing said signals received at said scattered andspecular photodetectors at a plurality of said selected locations toidentify variations in one of lubricant thickness, roughness, andabsorbing layer thickness in the disk.
 49. The apparatus of claim 47,wherein said analysis unit compares data received from a plurality ofselected locations at a first time and a second time to identifydifferences in one of lubricant thickness, absorbing layer thickness,and surface roughness of the thin film disk between said first time andsecond time.
 50. The apparatus of claim 49, further comprising: a motor,coupled to said disk receiver, for rotating said thin film disk.
 51. Theapparatus of claim 50, wherein said apparatus is enclosed in a containerto prevent substantially all external light from being received from oneof said scattered photodetector and said specular photodetector.
 52. Theapparatus of claim 45, wherein said collector further comprises a baffleto said scattered photodetector from receiving said scattered componentunless said scattered component reflects off an internal wall of saidcollector.
 53. An apparatus for measuring an absorbing layer thicknesson a thin film disk and for measuring a roughness of said thin film diskin a high temperature environment, comprising: light source means, fortransmitting a light signal toward a selected location of the disk at afirst angle, said first angle at an angle between vertical and ninetydegrees from vertical but not at substantially Brewster's angle of theabsorbing layer, said light source means capable of operating in thehigh temperature environment; polarizing means, disposed to receive saidlight signal, for selectively polarizing said light signal, saidpolarization one of a P linear polarization, an S linear polarizationand a combination of said P linear and S linear polarizations, saidpolarized light signal impinging upon the disk causing a specularcomponent of the polarized light signal to be reflected off of the diskat substantially said first angle and causing a scattered component ofsaid polarized light signal, said polarizing means capable of operatingin the high temperature environment; first receiving means, forreceiving said specular component from said selected location;collecting means, for collecting said scattered component in a collectorpositioned substantially adjacent to said thin film disk; secondreceiving means, for measuring said scattered component collected insaid collector; and roughness means, for determining the surfaceroughness of said thin film disk based upon said collected scatteredcomponent.
 54. The apparatus of claim 53, wherein the temperature of theenvironment is greater than sixty degrees Celsius.
 55. The apparatus ofclaim 53, wherein the temperature of the environment is greater thanseventy degrees Celsius.
 56. The apparatus of claim 53, wherein thetemperature of the environment is greater than fifty degrees Celsius.57. The apparatus of claim 56, wherein said scattered component includesonly those scattered components that have reflected at least once in thecollector.
 58. The apparatus of claim 56, further comprising: absorbinglayer thickness determining means, for determining a thickness of theabsorbing layer based upon the specular component of said polarizedlight signal.
 59. The apparatus of claim 58, wherein said absorbinglayer is comprised of carbon.
 60. The apparatus of claim 56, furthercomprising: analysis means, for comparing said specular and scatteredcomponents from a plurality of selected locations to identify variationsin said roughness and said absorbing layer thickness in the disk. 61.The method of claim 56, further comprising the step of: storage means,for storing first data relating to the absorbing layer thickness and theroughness of said thin film at a plurality of said selected positions ata first time and at a second time.
 62. The apparatus of claim 61,further comprising: analysis means, for comparing said first data withsaid second data to identify one of a change in absorbing layerthickness from said first time to said second time and a change in theroughness of said thin film from said first time to said second time.63. The apparatus of claim 62, wherein said analysis means includes:first identifying means, for identifying a first change valuerepresenting a change in said specular component of said S linearpolarized light signal between said first time and said second time fora plurality of said selected positions; second identifying means, foridentifying a second change value representing a change in said specularcomponent of said P linear polarized light signal between said firsttime and said second time for a plurality of said selected positions;third identifying means, for identifying when one of a change inabsorbing layer thickness and a change in the roughness of said thinfilm occurs between said first and second time based upon said firstchange value, said second change value, and the first angle.
 64. Theapparatus of claim 63, where said third identifying means includeshistogram means, for generating a concentration histogram including saidfirst change value and said second change value for a plurality of saidselected positions; and fourth identifying means, for identifying saidchange of absorbing layer thickness based upon said concentrationhistogram and the first angle.
 65. The apparatus of claim 64, whereinsaid concentration histogram identifies regions of said thin film diskhaving one of lubricant pooling, lubricant depletion, absorbing layerwear, and debris.
 66. The apparatus of claim 65 wherein said method isperformed in-situ.
 67. The apparatus of claim 56, further comprising:identifying means for identifying a first damage location havingsignificant surface roughness; and a high resolution means for analyzingsaid first damage location.
 68. The apparatus of claim 56, wherein saidlight signal is collimated.
 69. The apparatus of claim 56, wherein saidthin film disk is a silicon wafer.
 70. A method for measuring alubricant thickness on a thin film disk in a high temperatureenvironment, the thin film disk having an absorbing layer, comprisingthe steps of: (a) transmitting a light signal toward a selected locationof the disk at a first angle using a high temperature laser diode, saidfirst angle at an angle between zero degrees from vertical and ninetydegrees from vertical but not at substantially Brewster's angle of theabsorbing layer; (b) selectively polarizing said light signal using atemperature compensated quartz half plate, said polarization one of a Plinear polarization, an S linear polarization, and a combination of saidP linear and S linear polarizations; (c) said polarized light signalimpinging upon the disk causing a specular component of the polarizedlight signal to be reflected off of the disk at substantially said firstangle and causing a scattered component of said polarized light signal;(d) receiving said specular component from said selected location; (e)collecting said scattered component in a collector positionedsubstantially adjacent to said thin film disk; (f) receiving saidscattered component collected in said collector; and (g) determining thelubricant thickness based upon the specular component and said scatteredcomponent of said polarized light signal.
 71. The method of claim 70,wherein the temperature of the environment is greater than sixty degreesCelsius.
 72. The method of claim 70, wherein the temperature of theenvironment is greater than seventy degrees Celsius.
 73. The method ofclaim 70, wherein the temperature of the environment is greater thanfifty degrees Celsius.
 74. The method of claim 73, further comprisingthe step of: determining the surface roughness of said thin film diskbased upon said collected scattered component and said specularcomponent.
 75. The method of claim 73, further comprising the step of:determining a thickness of the absorbing layer based upon said specularcomponent and said scattered component of said polarized light signal.76. The method of claim 75, wherein said absorbing layer is comprised ofcarbon.
 77. The method of claim 73, wherein said scattered componentincludes only those scattered components that have reflected at leastonce in the collector.
 78. The method of claim 73, further comprisingthe step of: (h) identifying a plurality of locations on said thin filmdisk as the selected position; and (i) repeating steps (a) through (g)for each of said selected positions.
 79. The method of claim 78, furthercomprising the step of: comparing said specular components and saidscattered components received for a plurality of said selected locationsto identify variations in lubricant thickness on the disk.
 80. Themethod of claim 78, further comprising the step of: (j) storing firstdata relating to the lubricant thickness on the disk at each of saidselected positions at a first time; (k) repeating steps (a) through (i)at a second time; and (l) storing second data relating to the lubricantthickness on said thin film at each of said selected positions at asecond time.
 81. The method of claim 80, further comprising the step of:comparing said first data with said second data to identify a change inlubricant thickness from said first time to said second time.
 82. Themethod of claim 81, wherein said comparing step includes the steps of:identifying a first change value representing a change in said specularcomponent of said S linear polarized light signal between said firsttime and said second time for a plurality of said selected positions;identifying a second change value representing a change in said specularcomponent of said P linear polarized light signal between said firsttime and said second time for a plurality of said selected positions;and identifying when one of a change in lubricant thickness on said thinfilm occurs between said first and second time based upon said firstchange value, said second change value, and the first angle.
 83. Themethod of claim 82, where said step of identifying when one of a changein lubricant thickness on said thin film occurs includes the steps of:generating a concentration histogram including said first change valueand said second change value for a plurality of said selected positions;and identifying said change of lubricant thickness based upon saidconcentration histogram and the first angle.
 84. The method of claim 83wherein said method is performed in-situ.
 85. The method of claim 82,further comprising the steps of: identifying a first damage locationbased upon said scattered components and said specular components; andanalyzing said first damage location using a high resolution tool. 86.The method of claim 85, wherein said high resolution tool is one of anatomic force microscope and an optical microscope.
 87. The method ofclaim 73, wherein said light signal is collimated.
 88. The method ofclaim 73, further comprising the step of: focusing said light signalonto said selected location.
 89. The method of claim 73, furthercomprising the step of: focusing said polarized light signal onto saidselected location.
 90. The method of claim 73, wherein said thin filmdisk is a silicon wafer.
 91. A method for measuring a lubricantthickness on a thin film disk in a high temperature environment, thethin film disk having an absorbing layer, comprising the steps of: (a)transmitting a light signal toward a selected location of the disk at afirst angle using a high temperature laser diode, said first angle at anangle between zero degrees from vertical and ninety degrees fromvertical but not at substantially Brewster's angle of the absorbinglayer; (b) selectively polarizing said light signal using a temperaturecompensated quartz half plate, said polarization one of a P linearpolarization, an S linear polarization, and a combination of said Plinear and S linear polarizations; (c) said polarized light signalimpinging upon the disk causing a specular component of the polarizedlight signal to be reflected off of the disk at substantially said firstangle and causing a scattered component of said polarized light signal;(d) receiving said specular component from said selected location; (e)collecting said scattered component in a collector positionedsubstantially adjacent to said thin film disk; (f) receiving saidscattered component collected in said collector; and (g) determining thelubricant thickness based upon the specular component and said scatteredcomponent of said polarized light signal.
 92. The method of claim 91,wherein the temperature of the environment is greater than sixty degreesCelsius.
 93. The method of claim 91, wherein the temperature of theenvironment is greater than seventy degrees Celsius.
 94. The method ofclaim 91, wherein the temperature of the environment is greater thanfifty degrees Celsius.
 95. The method of claim 94, further comprisingthe step of: determining the surface roughness of said thin film diskbased upon said collected scattered component and said specularcomponent.
 96. The method of claim 94, further comprising the step of:determining a thickness of the absorbing layer based upon said specularcomponent and said scattered component of said polarized light signal.97. The method of claim 96, wherein said absorbing layer is comprised ofcarbon.
 98. The method of claim 94, wherein said scattered componentincludes only those scattered components that have reflected at leastonce in the collector.
 99. The method of claim 94, further comprisingthe step of: (h) identifying a plurality of locations on said thin filmdisk as the selected position; and (i) repeating steps (a) through (g)for each of said selected positions.
 100. The method of claim 99,further comprising the step of: comparing said specular components andsaid scattered components received for a plurality of said selectedlocations to identify variations in lubricant thickness on the disk.101. The method of claim 99, further comprising the step of: (j) storingfirst data relating to the lubricant thickness on the disk at each ofsaid selected positions at a first time; (k) repeating steps (a) through(i) at a second time; and (l) storing second data relating to thelubricant thickness on said thin film at each of said selected positionsat a second time.
 102. The method of claim 101, further comprising thestep of: comparing said first data with said second data to identify achange in lubricant thickness from said first time to said second time.103. The method of claim 102, wherein said comparing step includes thesteps of: identifying a first change value representing a change in saidspecular component of said S linear polarized light signal between saidfirst time and said second time for a plurality of said selectedpositions; identifying a second change value representing a change insaid specular component of said P linear polarized light signal betweensaid first time and said second time for a plurality of said selectedpositions; and identifying when one of a change in lubricant thicknesson said thin film occurs between said first and second time based uponsaid first change value, said second change value, and the first angle.104. The method of claim 103, where said step of identifying when one ofa change in lubricant thickness on said thin film occurs includes thesteps of: generating a concentration histogram including said firstchange value and said second change value for a plurality of saidselected positions; and identifying said change of lubricant thicknessbased upon said concentration histogram and the first angle.
 105. Themethod of claim 104 wherein said method is performed in-situ.
 106. Themethod of claim 103, further comprising the steps of: identifying afirst damage location based upon said scattered components and saidspecular components; and analyzing said first damage location using ahigh resolution tool.
 107. The method of claim 106, wherein said highresolution tool is one of an atomic force microscope and an opticalmicroscope.
 108. The method of claim 94, wherein said light signal iscollimated.
 109. The method of claim 94, further comprising the step of:focusing said light signal onto said selected location.
 110. The methodof claim 94, further comprising the step of: focusing said polarizedlight signal onto said selected location.
 111. The method of claim 94,wherein said thin film disk is a silicon wafer.